Is it possible for a US party to refuse to let someone run for office under their party banner?

This is Trump-related, since he has now made some noises about running as an independent. And there are purportedly a whole lot of establishment Republicans who are horrified of the idea of him as their nominee.

So, could the party announce that he WILL NOT be the Republican candidate, even if he wins the most primaries, delegates, etc.? Can they enforce it?

No. We don’t have Euro-style cadre parties with party dues and membership cards and hierarchical organization. There is no mechanism for expulsion from either major party. It’s more of an individual-entrepreneurial model. David Duke is a Republican if he says he is, Lyndon LaRouche is a Democrat if he says he is, and either can run for his chosen party’s nomination, however embarrassing that might be to the party leadership, to the extent either party has one at all. There is some party discipline among legislative caucuses, but otherwise there is no discipline by a party as an institution – Priebus cannot make any Republican do anything or not do anything.

Perhaps all of the above needs to change.

It wouldn’t have to be ‘expulson’, it would be “we won’t let you run for office as our candidate”.

For instance, they could conceivably refuse to seat delegates at the convention who are pledged to Trump – unless there are rules about seating delegates that would prevent this. And I imagine that such a decision could cause even more chaos and disharmony than a Trump numination would.

So maybe it’s politically impossible to to, but is it procedurally impossible to do?

Stephen Colbert was not allowed a place on the 2008 SC Democratic Presiential primary ballot by state party leaders. So, the answer is apparently ‘yes’ for local or state divisions of the political parties (who actually control who appears on primary ballots) but perhaps not on the national level.

On occasion, a party has refused to provide funding or any other support for a candidate who wins a nomination, instead either supporting one of the stalwarts running as a temporary independent, or sitting it out - the Republicans with David Duke for Senate in Louisiana comes to mind.

Massachusetts Democrats won’t provide support for a *primary *candidate who doesn’t get at least 15% support at the state convention, no matter what the voters might subsequently want.

If he gets as far as winning a majority of the delegates, he basically is the party.

I think it would be possible as a practical matter. As posted, if someone says, “I’m a Republican,” and they’re running for office, then no, the party can’t “throw him out” of the party. But, the party can deny funding from the national committee, and basically disavow the candidate, in effect saying, “This guy doesn’t speak for the Republican Party, he’s not getting any of our support.” In other words, someone can be an unauthorized party candidate.

No, that’s not what I’m talking about. I’m talking about keeping someone off the ballot altogether, or at least off in terms being affiliated with the party names.

Stephan Colbert is a joke, or at least his campaign was. Colbert didn’t qualify per the state Democrat Party primary rules.

For the presidential level, there would be 51 different sets of answers in the detail you want.

If Trump were to win the most primaries, and has the most state-awarded delegates, he would be the party’s nominee.

Could the Democrat Party have chosen Hillary over Obama, in spite of Obama having gained more delegates? No, they could not.

If I remember correctly, the delegates for both parties primaries are only tied to their state-authorized delegates for the first vote. After that, delegates could change their allegiance (with a wink and a nod from their home state party bosses).

What about faitheless electors?

edit: I know that wouldn’t affect who was on the ballot, but would affect who got electoral votes.

*Really? *

Which “Democrat [sic] Party primary rules” did he not qualify?

Colbert’s Presidential Bid Ends After a ‘No’ in South Carolina

With so many candidates splitting the delegate vote he probably wouldn’t get a majority. Then the party leaders could get together in smoke filled rooms and pick anyone else they want.

As mentioned, it’s the *state *parties that control entry in the primaries and presence in the ballot under their flag, and in many cases it’s pretty much a tick-off-the-checkboxes process while in others there may be a vetting heavily influenced by how much does your state party want to piss off a potential future candidate/President or the National Committee or the big donors or combinations thereof; but in anycase you cannot simply blackball someone a priori. Notice the Colbert case mentioned above - it boiled down to the state party council saying “obvious joke is joking”. Being an absurd candidate did not prevent Michelle Bachmann from campaigning last time around.

Independent/“Third” Party candidates, OTOH, can and do face hurdles from the state Secretaries of State or Election Commissioners, who are all elected or appointed under the aegis of one of the two major parties.

To answer the OP
Washington State Grange vs. Washington State Republican Party answered which trumps which, a person’s right to associate with a political party for the purposes of running for office OR the party’s right to disassociate itself from the candidate by not letting them run as a member of the party. The 7-2 decision handed down by SCOTUS was

The candidate can choose which party to associate with over the wishes of “the Party”. Thus the RNC or state committee cannot stop Trump from running as a Republican. Him running under the Republican label indicate the party he associates with and does not imply the RNC/State committee endorses him

If Trump won the nomination, the best the national RNC could do is go through the 3rd party ballot process and make Jeb Bush the “Republican” candidate endorsed by the national party.

But that would tear the party apart. There’s already tension between the grassroots and the Beltway establishment. If the RNC didn’t support the Presidential nominee chosen by the party’s voters it would turn into open warfare.

Much as with Goldwater, the RNC would just have to back Trump and hope that it only means a loss in this election and not longterm damage.

I do not think that this correct. In California Democratic Party v. Jones, the Supreme Court upheld a political party’s First Amendment associational right to candidate selection, and when a primary process selects the party’s candidate, the party has the right to limit the candidates running for that party’s nomination.

Washington State Grange examines a slightly different process, in which the primary election is not party based, but in which the two highest vote-getters are selected for the general election, regardless of their party affiliation. The Supreme Court said that in such a system, a candidate could identify him- or herself with any party he or she selected because it wasn’t an endorsement or nomination from the party.

It’s a subtle difference, but what it means is that where a nonpartisan primary election is for an open spot in the general election, a political party cannot refuse to let a candidate identify him- or herself as aligned with that party, but where the primary is to select the party’s candidate, the party can limit candidates.