What made the nuclear option this time around so tenable, as [o]pposed to say 2005?
It appears to have been a combination of frustration and desperation. A PolitiFact article, November 22, 2013, that discusses Sen. Reid's "flip-flop" on the "nuclear option".
[While only excepts are provided, reading the full article is suggested.]
We’ll take a look back to 2005, when the partisan lineup was substantially different. President George W. Bush had recently won a second term, while his fellow Republicans had a majority in the Senate. [...]
In the Senate, the Democratic minority had filibustered a number of Bush’s judicial appointments, displeasing Republicans, who seriously considered implementing the nuclear option that would allow them to confirm judges with a simple majority.
Fast-forward to 2013. Now, Democrats held the White House and a Senate majority. The Republican minority had been stalling nominations and appointments by Obama, including filibustering the nomination of former Republican Sen. Chuck Hagel for secretary of defense. Senate Democrats decided to go nuclear after the Senate GOP made clear that they had no intention of allowing three vacancies on the U.S. Court of Appeals for the District of Columbia Circuit to be filled.
At that point, Senate Democrats took the opposite view they had taken in 2005. Led by Majority Leader Reid himself, they successfully invoked the nuclear option in a near-party-line vote, 52-48.
Before the vote, Reid explained his plan on the Senate floor: "The Senate is a living thing, and to survive it must change, as it has over the history of this great country … This is not about Democrats versus Republicans. This is about making Washington work — regardless of who is in the White House or who controls the Senate," Reid said.
Then he added: "It is time to change the Senate before this institution becomes obsolete."
Republicans, by frustrating Reid's ability to guide to Senate to confirm to Obama's nominations, forced Reid's hand thus daring him to pursue the "nuclear option".
GOP's existential test: Why they're really escalating a nuclear option crisis, November 20, 2013 (The day before the nuclear option was used.)
If they call Harry Reid's bluff, they get to preserve the existing ideological balance on the court, which wouldn't be a bad outcome for them at all given how much power that court wields over Obama's regulatory regime.
But because the answers to the above questions [see at the source] are so obvious, Republicans must know they've put Harry Reid in an impossible position. It would be an act of political negligence, and of negligence to the constitution, for him to allow the minority to nullify vacant seats on the judiciary, simply to deny the president his right to leave an ideological imprint on a court. The logical extension of the GOP position -- that “there is no reason to upset the current makeup of the court" -- is a semi-permanent suspension of all appellate and Supreme Court confirmations. A permanent filibuster, undertaken in the hope that, through retirements, the courts will wither into more favorable balance.
That's clearly untenable. Republicans know they've given Reid practically no choice. And if he goes nuclear it might prove to be an even better outcome for them. It will provide them a plausible rationale for taking things a step further if they win back the Senate in 2014. Getting Democratic fingerprints on the nuclear rule-change precedent, will provide Republicans the cover they'll need to eliminate the filibuster altogether in January 2015.
While the above deals with Sen. Reid's frustration, the following deals with the desperation to protect the laws passed by Democrats by selecting "preferred" judges for the federal courts. At the time, there was widespread "dislike" of the Affordable Care Act and some other legislation passed by the previous filibuster-proof Congress. Having lost the House to Republicans, Reid was faced with the possibility that the Senate could become a Republican majority in the next election. (It happened.)
Partisanship in Judicial Selection
Last year, in response to Donald Trump’s claim that an adverse judicial ruling was wrong because it was issued by an “Obama judge,” Chief Justice John Roberts replied that the federal judiciary does not consist of “Obama judges or Trump judges, Bush judges or Clinton judges.” Noting the importance of an independent judiciary, Roberts characterized all of his fellow federal jurists as “an extraordinary group of dedicated judges doing their level best to do equal right to those appearing before them.” (Verdict)
Despite this claim by CJ Roberts, there are, nonetheless, judges who lean left or lean right. Partisans in the Senate know and understand that — they don't often publicly admit it.
The Politics of Selecting the Bench from the Bar: The Legal Profession and Partisan Incentives to Introduce Ideology Into Judicial Selection
The implications of a politicized judiciary in a polarized era of American politics have been a matter of considerable interest. Reflecting the notion that the courts will take on an expanded policymaking role during periods of intense legislative gridlock [...], recent years have seen U.S. courts determine state and national policy on some of the most politically charged controversies of the day, including affirmative action, health care reform, and same-sex marriage. The business of selecting judges has also become ideologically contentious, both at the state and federal levels. The American Bar Association (ABA), for example, has long maintained that judges should be chosen strictly on “merit-oriented” criteria, while many on the right have challenged whether the ABA is truly non-partisan and emphasize the need to correct for political imbalances in the legal community. These battles have gone all the way to the White House. In 2001, for example, the George W. Bush Administration announced that it would no longer rely on what it perceived to be liberally biased ABA judicial ratings, while Democrats sided with the ABA and accused Bush of interjecting politics into judicial selection. More recently, the administration of Donald Trump has followed the example set by the Bush Administration in declaring that the ABA would not be consulted in the selection of federal judges.
George W. Bush and Donald Trump used recommendations from the Federalist Society for judicial appointments.
The role of federal judges is to apply an interpretation of the Constitution to challenges to laws. Political parties want judges who would be more likely to interpret the Constitution more favorably to their ends — to uphold their laws. Given that such appointments are for life, having judges on one's side helps to ensure such laws will not be overturned easily.
At the heart of the use of the "nuclear option" were three appointments to the United States Court of Appeals for the District of Columbia Circuit. Short of the Supreme Court, who better to protect the laws and legacy of Democrats until they have become "settled law" and unlikely to be overturned?
United States Court of Appeals for the District of Columbia Circuit
The D.C. Circuit's prominence and prestige among American courts is second only to the U.S. Supreme Court because its jurisdiction contains the U.S. Congress and many of the U.S. government agencies, and therefore it is the main appellate court for many issues of American administrative law and constitutional law. [Emboldening added.]
Nuclear option - Rationale for change
The Democrats' stated motivation for this change was expansion of filibustering by Republicans during the Obama administration, in particular blocking three nominations to the United States Court of Appeals for the District of Columbia Circuit. Republicans had asserted that the D.C. Circuit was underworked, and also cited the need for cost reduction by reducing the number of judges in that circuit. [Emboldening added.]