For example, a Prime Minister is voted by the party, so if they were to switch parties they would not be the leader of the other party. They have a function within their party.

But is the party of the US President anything more than a label?

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    In UK at least, he'd still be prime minister until a vote of no confidence unseated him
    – Ne Mo
    Mar 6, 2017 at 16:58
  • Is that so? I would have thought the party with the most seats would present their deputy as the new Prime Minister, while the PM crossing the aisle would continue as a Member of Parliament for their new party. Mar 6, 2017 at 17:04
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    Keeping it to UK, the PM is technically appointed by the sovereign. The crown is supposed to ask the leader of the largest party first, and they always have, but occasionally they decline. In 1924 conservatives remained the biggest party but Baldwin resigned after election regardless. Crown appointed leader of Labour, 2nd biggest party, James McDonald. However, a government can always be dissolved by a vote of no confidence in parliament. That would probably happen in the circumstances you're describing.
    – Ne Mo
    Mar 6, 2017 at 17:28
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    Just to add, the drafters of the Constitution way back when deliberately tried to create a non-partisan system, in the belief that parties would compromise the nation's unity.
    – AAM111
    Mar 6, 2017 at 22:11
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    @JFA unless your name is Winston Churchill, who switched party twice and on the second occasion said "anyone can rat, but it takes a certain ingenuity to re-rat."
    – nigel222
    Mar 7, 2017 at 17:48

4 Answers 4


Pretty much just a label. Obviously though if you switch your label it causes a big uproar with your constiutents. This hasn't ever happened with the president before, but it has happened with sitting senators. Most recently Senator Arlen Specter switched parties from Republican to a Democrat on April 28, 2009 (in the middle of his term). He stated that

As the Republican Party has moved farther and farther to the right, I have found myself increasingly at odds with the Republican philosophy and more in line with the philosophy of the Democratic Party.

He then switched his party and ran the next election as a Democrat (and lost).

  • There were some switches D to R as well in the House of Representatives; Republicans tried to spin it as a Big Deal but I don't recall it having any meaningful larger effect.
    – user4012
    Mar 6, 2017 at 16:44
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    Also, we shouldn't forget that Trump was a Democrat before 2008 (granted, he didn't yet hold an office when he switched). Same goes for Mike Bloomberg in NYC mayoral elections, he switched from D to nominal "R" to run there.
    – user4012
    Mar 6, 2017 at 16:46
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    @user4012 - Most notable of those was probably Zell Miller who was initially a pro-segregation Democrat. He never officially switched parties, but he quit trying to run as a Democrat after his 2002 race, by which time that entire wing had already switched to the Republican party, and has endorsed only Republicans nationally since then. He's one of the only people known to have been a keynote speaker at both Republican and Democratic conventions (2004 and 1992 respectively).
    – T.E.D.
    Mar 6, 2017 at 21:51
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    In the case of Arlen Specter, PA residents were bombarded by ads containing video of him saying "I switched parties to get reelected" over and over again. I remember those ads vividly and I didn't even live in PA at the time, just visited.
    – mao47
    Mar 7, 2017 at 20:00
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    It's also worth noting that Specter proposed a Senate rule to penalize party switchers in 2001, when a Sen Jeffords from VT switched from Republican to Independent and caucused with the Democrats, giving them a 51/49 control of the Senate
    – Machavity
    Mar 7, 2017 at 21:00

Party in the USA is no more than a label for anyone.

Party affiliation is just a box you check when you register to vote. Its only real practical effect is that it allows you to vote in primary elections for the party you have selected*. Some states have restrictions on how often you can switch (to prevent partisans from purposely polluting the other party's primaries), but other than that, there are no restrictions on switching parties.

The parties don't have any say in who their constituents are either, or even over who runs as a candidate in their primaries. For instance, when I lived in Pennsylvania in the 90's, followers of Lyndon LaRouche used to show up on every primary ballot in my small Borough. They'd typically have very bland non-ethnic looking names, supposedly in hopes that low-information voters would pick them just based on name. My local party officials strenuously objected to this, but all they could do was post someone outside the official campaigning limit with sample ballots to hand out, and in particular pointing out which candidates were the LaRoucheites.

The point of this is that parties really have no control over who runs under their banner, or even their own membership.

* - For this reason, the only thing a person registering "independent" is really accomplishing in the USA is ensuring they have no say in who is running in the general election. However, even this isn't always the case. For example, the Democratic Party in Oklahoma currently allows independents (but not Republicans) to vote in its primaries. Minnesota (h/t to @SethR) doesn't even have official party membership.

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    As an unrelated note, I'd like to add that a USA political party is really more analogous to a "Coalition" in Parliamentary Democracies, not what they call a "party". The difference is that in PD's, the two coalitions are formed after the election, while in the USA the coalitions are entered into before, and then the voters decide which of the two will be the ruling coalition, and which will be in opposition.
    – T.E.D.
    Mar 6, 2017 at 19:11
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    In some states you don't even register with a party. Here in Minnesota, for example, there is no box to check when you register to vote. At caucus time (we are now a caucus state, as opposed to having primaries), you just show up at the party caucus you want to support. They all happen at the same time, so it would be very difficult to go to more than one.
    – Seth R
    Mar 6, 2017 at 19:48
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    @SethR - Legit. I added it to the footnotes in the answer.
    – T.E.D.
    Mar 6, 2017 at 21:56
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    @BigDataLouis - I have in the past heard of a party offering leadership positions as an inducement for switching when it was close to a tie. I suppose if the Speaker were a person they thought they could sway, that position might be offered. It would be weird to have someone that potentially disloyal as Speaker though.
    – T.E.D.
    Mar 6, 2017 at 22:58
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    Political parties are private clubs and can exclude anyone they want. The primary system may limit that, but only if the party agrees to use it. In the caucus states the parties run their own caucuses and set their own rules. However, even in primary states the party may be able to reject candidates. For example, when Stephen Colbert tried to register as a Democratic candidate for President in the South Carolina primaries for the 2008 election he was rejected by that state's Democratic Party Executive Committee.
    – Ross Ridge
    Mar 7, 2017 at 2:25

Not quite the same as the President switching parties, but former President John Tyler was disowned by his party (the Whigs) in 1842. He did not switch parties, but instead was independent for the remainder of his term. From Wikipedia (emphasis mine):

On September 13, when the president did not resign or give in, the Whigs in Congress expelled Tyler from the party. Tyler was lambasted by Whig newspapers and received hundreds of letters threatening his assassination. Whigs in Congress were so angry with Tyler that they refused to allocate funds to fix the White House, which had fallen into disrepair.

  • 1
    A nuance I know, but from reading through that entire entry, it looks like he officially "expelled", but rather driven out. If he didn't mind the abuse (and losing his next primary) he could have stayed.
    – T.E.D.
    Mar 7, 2017 at 14:17

In addition to the other examples mentioned in other answers, Teddy Roosevelt did switch to the Bull Moose party, but that was after he finished his term.Wiki link

More recently, for the 2016 presidential election, the Republican primary requested a "loyalty oath" consisting of the text:

“I, ________, affirm that if I do not win the 2016 Republican nomination for President of the United States I will endorse the 2016 Republican presidential nominee regardless of who it is.” ... “I further pledge that I will not seek to run as an independent or write-in candidate nor will I seek or accept the nomination for president of any other party.” (Source:)

I am not a lawyer, so I can't say how "run" is defined (as in does it just mean be in the running for election, or does it also included being the president afterwards), but there could be some arguments that this loath would preclude becoming independent or another party at least during the current term.

(Note that I picked on the 2016 Republican loyalty oath because it was the easiest to find (because at one point, questions on whether Trump would sign it was a hot topic) but I believe both major parties have had similar things in previous years as well (although a quick search suggests it being more common thing on the Republican side but I don't have a strong citation there))

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    The oath is not a legally binding document in any way shape or form. Its just so that if you break the oath there will be an official and clear record that you are an oath breaker and people shouldn't trust you. Mar 6, 2017 at 18:34
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    "I will endorse the 2016 Republican presidential nominee regardless of who it is" -- Wow, forcing such a promise on a candidate is pretty bad. Mar 6, 2017 at 19:43

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