Have other countries with similar supreme courts found a way to reduce
this polarization within the court?
It turns out that this doesn't have a simple mechanical answer. Naively similar systems with common legal roots often work very differently in practice. And, there are quite a few factors that influence the outcome.
In general, the factors that promote a less partisan judiciary are:
Merit based civil service appointments of career judges who start at the bottom and are promoted from within the judiciary, as opposed to elected judges or judges whose appointments are purely political appointments.
Judges who are less competent relative to the average and least competent elected officials (causing the system over time to trust judges less relative to elected officials to make hard decisions). Both the competence of judges and the competence of elected officials impact this factor.
A comparatively narrow range of political and cultural opinions in the jurisdiction that the court presides over.
Weaker judicial review powers, especially with regard to public law issues. Further, ordinary courts are less partisan when judicial review and/or public law questions are confined to specialized courts.
A parliamentary system of government as opposed to a strong President system (for multiple reasons discussed below).
A unitary as opposed to a federal system of government (by providing one less area of judicial resolution of political conflicts).
A history of the highest court having been subordinate to another court during the period in which its institutional norms were developed.
Constitutional protections of rights, and entrenched treaties and/or legislation, that are easier to amend or abrogate.
It is also worth observing that judicial partisanship is not static. It changes over time as the relevant factors change.
For example, Canada's Supreme Court was much less partisan when its was subordinate to the Judicial Committee of the Privy Council of the House of Lords and has no judicial review authority, as was the case prior to 1949, than it was after 1982 when it was both the highest court in the land, and was given judicial review authority to implement the Canadian Charter of Rights and Freedoms.
Another point worth noting is that partisan decision-making can, but does not necessarily, imply that court rulings often involve split decisions in the way that it does on the U.S. Supreme Court. Where there are frequent split decisions, partisanship is largely a function of how stable the coalitions of judges on each side of the splits tend to be.
But, a court can be extremely partisan and political in its decision-making despite almost always having unanimous decisions or lopsided majorities, if one party have managed to secure a dominant position in the makeup of the court.
Three Other Common Law Systems
Another answer has addressed the U.K. system so I will only address that in passing, but other systems based on the common law legal systems of the U.K. are particularly comparable to the U.S. Australia, Canada and India illustrate that these similarities don't necessarily produce similar levels of judicial partisanship. All three of these examples, like the U.S. and unlike the U.K. prior to Scottish and Northern Ireland's autonomy, are federal systems.
Canada's courts do frequently make political public law decisions in a manner similar to that of U.S. courts based upon its constitution and have a fairly political appointment process to higher appellate courts. But, there are a couple of factors that make the political divide less intense.
One is the "notwithstanding clause" that gives the legislature the power to intentionally violate protections set forth in its Charter of Rights and Freedoms, so long as it does so openly, which discourages the courts from interpreting those rights in a manner that does not have meaningful public support.
Another is the reality that while there are absolutely partisan differences of opinion in Canadian politics, that there is far less of a chasm of completely different cultural and political values and world views in Canada than there is between the left and the right in the U.S. With a narrower range of cultural and political values, its partisan fights are more subtle and often not so vitriolic.
Canada has a parliamentary system and civil service appointments of many judges, (although the appointment process of top judges in Canada has been somewhat more partisan than in Australia, discussed below, in part, because Canadian Supreme Court judges have more judicial review power than in Australia).
In Australia, whose federal system and common law legal tradition are superficially similar to the United States, has fewer formal protections for individual rights in its federal constitution than the United States. So, much of its high profile constitutional jurisprudence involves federal limitations on the powers of federal and state governments respectively, and more "mechanical" aspects of its constitution that are rarely litigated in the U.S., that are employed in a rights protecting manner. This is much less nakedly partisan.
Australia, like Canada, is a parliamentary system with civil service appointments for judges, points that are discussed below. Australia, like Canada, also has a fairly narrow range of political and cultural views compare to the U.S., despite the fact that it does have partisan differences.
On the other hand, India, which, like the U.S. has a very broad span of cultural and political values, a powerful national Supreme Court in the common law tradition similar to that of the U.S. and a fairly political system of judicial appointments has a judiciary that is every bit as partisan and controversial as that of the U.S. (if not more so because in India, the Supreme Court can even declare some provisions of the constitution to be unconstitutional).
Another factor in this partisanship is that it takes a more politically connected and ambitious individual eager to exercise power to make it to the very pinnacle of a judicial system in a country of about 1,339,000,000 people with intense partisan divides that have led to civil war in not so distant history that still has more than one active insurgency in progress (India), than in one with 37,060,000 people (Canada), or 24,600,000 people (Australia) which have relatively tranquil political histories in which citizens have far more common ground.
The impact of this partisanship in the courts of India is limited primarily by the reality that courts in India are even more byzantine than those in the U.S., so the judicial process is slower, less predictable, and its rulings are somewhat less faithfully implemented in day to day life than in the U.S. India does, however, have a parliamentary system with impacts discussed below. These factors make it a less attractive forum for resolving political disputes with short fuses timewise.
A History Of Judicial Subordination
As an aside, all three of these systems historically had a highest court of review in the Judicial Council of the Privy Council of the U.K. House of Lords, although all of them have discontinued this judicial branch linkage to the U.K. system (Canada in 1949, India in 1950, Australia in 1968).
The tradition of having a highest national court that was subordinate to the highest court of another country helped build a tradition of non-partisanship that was well ingrained by the time that these high courts became independent which was absent in the U.S. whose courts have been independent of any other country's since the Revolutionary period.
Judicial Appointment And Promotion
The Civil Service Appointment Norm
Also the vast majority of countries (e.g. England, Australia, France, Italy, Poland) appoint judges through a merit based civil service process and frequently appoint newly hired judges to low level trial courts handling small claims and minor criminal offenses and then fill more senior judicial posts such as general jurisdiction trial courts and appellate courts by promoting judges from lower level posts within the system, and appearing to be political in decision-making will often cause a judge to not be promoted. At the higher appellate level, the judges will often have been appointed to their first positions in the judicial branch decades earlier and often many elections ago.
These systems still vary quite a bit in the extent to which decisions on which judges are promoted are political, especially at the highest appellate levels. For example, the U.K. has tended to be more partisan, while the promotion process in Poland has recently become much more partisan.
The Political Appointment Norm In The U.S.
The U.S. in contrast, is almost unique in the world in having many elected judges (as many are at the state and local level, not infrequently with partisan nominations for candidates). And, it is unusual in the respect that federal judges as well as a significant number of state judges are pure political appointments, typically of politically connected distinguished practicing lawyers in mid- to late- careers as lawyers, who are frequently appointed directly to higher courts without working their way up to ranks after starting at the bottom. Needless to say, neither of these approaches to filling judicial posts is not well suited to an apolitical judiciary.
Other Distinctive Consequences Of The U.S. Judicial Appointment System
Not only does the U.S. system of judicial appointments produce judges who are more ideologically partisan, it also produces judges who are well connected, have a better understanding of the inner workings of the political process, and are overall more formidable and ambitious individuals who have taken big career risks in life to become notable enough to be considered for appointment, who are more comfortable exercising considerable power.
Fundamentally, ordinary court judges in most countries are basically senior civil servants who are often attracted to the profession by an idealist motive to administer the laws fairly in a fairly naive "good government" sense, who have frequently done little to really distinguish themselves professionally or politically before becoming judges who aren't any more politically connected than other senior civil servants.
In contrast, American judges are, as often as not and especially in more important trial courts and appellate courts, activist forces of nature who enter the profession as a second career with a political agenda as a significant motivation.
The Impact Of The Character of Judicial Appointees On Judicial Power
Also, because political parties are so weak in the U.S. compared to other countries, and because there are so many elected offices in the U.S., there is a lower minimum threshold of competence of elected officials in the U.S. and the average competence of U.S. elected officials in lower offices is comparatively poor. Most countries have political parties that can and do actively screen would be candidates for competence on a basis similar to job applicants, there are fewer posts to fill via elective office than in the U.S., and those officials once elected are more accountable to their political parties and have less independent political power at lower levels (where they are expected as local government elected officials or rank and file members of state or national parliaments, expected to tow the party line).
This reality interacts with the the comparatively formidable nature of U.S. judges, almost all of whom except at the very lowest levels, are successful law school graduates. Basically, in the U.S. the least competent judges are much more competent and intelligent than the least competent elected officials and the average judge is likewise more competent than the average elected official of governments that come before them. Over time this has encouraged the legal system and legislation to give more power to judges relative to elected officials. In contrast, in most other countries where there is far less of a gap in competence between elected officials who are making decisions that are reviewed by judges and the judges themselves - in most countries elected officials are more competent on average and at the bottom end of the range, and judges are moderately less formidable, than in the U.S., there has been far less of a tendency to prefer judicial decision making to legislative decision making for questions for sensitive complex analysis is necessary in making a policy decision.
Differing Approaches To Judicial Review of Legislation
A large share of the highly political cases in the U.S. involve questions of what is known as "public law" interpreting limitations on the rights of government relative to individuals and other governmental bodies, as opposed to "private law" governing the legal relationships between private individuals such as contract law and the law governing personal injury lawsuits.
In many countries, all or most of these cases are removed from the ordinary courts and reserved for a special "constitutional court" (e.g. in Germany) whose appointees are more political than the ordinary courts, or an entirely different court system, such as the "Council of State" in France and Belgium, which are staffed by elite civil servants. Many of these countries also have very large numbers of judges on their highest courts (often several dozen) who usually hear cases in subject-matter specialized divisions, diluting the power of any one judge's partisan views. This makes the ordinary courts far less partisan, in part, by shifting the controversial cases elsewhere.
Usually, in these systems (and also, for example, in the English courts), ordinary courts do not have the power of judicial review that American courts do (i.e. they cannot declare laws invalid unless they directly contradict each other and the court has to determine which one prevails over the other), giving them considerable less discretion.
Indeed, in the U.K., the highest judicial authority was a committee in the House of Lords which was part of the legislature until the very recent formation of the Supreme Court of the U.K. in 2009, and the absence of judicial review was a principle known as parliamentary supremacy.
More recently, this has shifted somewhat as many countries, particularly in Europe (not just the E.U., especially through the Council of Europe), have adopted international human rights treaties whose provisions are incorporated into domestic law and give either special public law courts, or ordinary courts, or both, the power to invalidate ordinary laws that conflict with them.
Put another way, very few countries had a separation of powers between the legislative branch and the judicial branch until the post-WWII era when the experiences of the war years caused a widespread desire to entrench individual rights protections vis-a-vis the government and to enforce that with a form of judicial review that is grafted into a system not really designed to do that in something of a constitutional kludge.
In contrast, in the U.S. a feature of the judiciary that isn't widely understood, but is important to understand when comparing judicial systems, is that in U.S. jurisprudence, the authority to declare laws unconstitutional is not just a power reserved to the U.S. Supreme Court. Every single judicial branch judge in the U.S., from a municipal traffic court judge to a state trial court judge in a death penalty case to intermediate state appellate court judges to state supreme court judges to a federal district court judge considering a civil rights lawsuit at the trial court level to intermediate appellate court judges in the federal system has the power to declare a law pertinent to a case before them unconstitutional (and unlike many other countries, no U.S. court has the authority to declare a law unconstitutional in the abstract as opposed to in a lawsuit brought by someone affected by the law).
Also many of the highly political cases arise under the U.S. Constitution so neither the President or legislature can overrule a final decision of the judicial branch on issues of constitutional law, and amending the constitution is very hard (in contrast, amending the constitution in most countries is comparable in difficulty to amending a state constitution in the U.S.) giving the judiciary in the U.S. far more power than in many systems. This reality is particularly important because the U.S. system is both federal and is Presidential rather than parliamentary, which is important for the reasons discussed below.
Fusion Between The Executive And Legislative Branches And Unitary Governments
Most countries also have far less of divide between the executive branch and legislative branch, which are fused in parliamentary systems (such as the U.K., Germany and Italy).
Also, many countries either have unitary governments (e.g., the U.K. until recently, as well as France, Poland, Italy, and New Zealand), or at least, have a unified court system even if there are both state-like and national governments in the legislative and executive branches (e.g. in Germany, the lower level courts that administer national law except for high level appeals are run by state governments. This removes potential for conflicts between state and national laws that must be resolved by courts putting political footballs in their hands.
The lack of separation of powers is significant not just because it prevents court fights between the executive branch and the legislature. It also means that the vast majority of the time the cabinet which is accountable to the parliament has more or less absolute power to enact any law that the ruling party or coalition supports.
This has the practical effect of drafting laws in a very different manner than one would in a U.S. style bicameral strong President system. In the U.S., laws are frequently drafted in a manner that is intentionally ambiguous intentionally punting hard issues to the courts, in order to secure their passage on a law by law basis.
This also changes the attractiveness of public law litigation as a political tool. In countries with parliamentary systems, if the current government doesn't like the law, or there is controversy regarding what the law means, the route of least resistance is frequently to simply change the law or to clarify it, because the ruling government almost always has the power to do so, which makes litigation over ambiguous legislation much less of a useful tool for opponents of the government.
In contrast, in U.S. style systems, the status quo (which is determined by the courts) is much more powerful because passing new legislation is much more difficult for reasons including bicameral legislatures (which may be controlled by different political parties as Congress is right now), supermajority requirements to pass legislation (especially in the U.S. Senate where the filibuster created a de facto 60% majority requirement to take most actions until the last few years), and the Presidential or Gubernatorial veto power (sometimes exercised even when the legislature is controlled by the same party as the executive because the executive is not accountable to the legislature).