Assuming Trump is the GOP nominee...will 2nd place in the primaries endorse him?

[Mr. Morden]

?

[Mr. Morden]

If someone else actually ends up winning delegates, they'd have to REALLY hate Trump...

Past primary challengers to incumbent presidents who actually made it on the ballot in most states (Reagan '76, Kennedy '80, Buchanan '92) all ended up endorsing the president they were running against in the general election.

That said, Trump is a weird case.  ~1/5th of the GOP caucus in the Senate didn't endorse him in the GE last time, and he won anyway.

Also, if, say, Kasich is running against Trump in 2020, the question will be posed both ways: Kasich will be asked if he'll endorse Trump in the GE if Trump is nominated, and Trump will be asked the same of Kasich if Kasich is nominated.  I doubt Trump agrees to endorse Kasich in the unlikely event that Kasich is nominated, so Kasich might just reciprocate and say he wouldn't endorse Trump either.....

How the RNC chair responds to candidates refusing to pledge support for the party regardless of who win the nomination, I don't know.  Aren't there even some state primaries where such a pledge is required for ballot access?

[Mr. Morden]

Did Randall Terry and John Wolfe endorse Obama? I don't think so...

OK, edited my previous post to say that past primary challengers who actually made it on the ballot in most states have tended to endorse the winner.  I don't think any of the primary challengers to Bush '04 or Obama '12 made it onto the ballot in more than a handful of states.

My *guess* is that at least one person will be challenging Trump in the primaries who will have enough of an organization to get ballot access in more than half the states.  I think even a McMullin could pull that off.  That's my guess, but I wouldn't call it a sure thing....

[Mr. Morden]

Did Randall Terry and John Wolfe endorse Obama? I don't think so...

My *guess* is that at least one person will be challenging Trump in the primaries who will have enough of an organization to get ballot access in more than half the states.  I think even a McMullin could pull that off.  That's my guess, but I wouldn't call it a sure thing....

I think there will be several challengers. Kasich, Cruz, Martinez, McMullin and maybe even Romney.

I don't know.  Barring extraordinary circumstances, there are only going to be so many voters willing to vote for a non-Trump candidate in the GOP primaries, and once one challenger announces their candidacy, it might deter others from jumping in and diluting the anti-Trump vote.  We'll see.  Or multiple candidates might begin the race, but only one would get enough traction to merit staying in the race once the voting starts.

Most likely scenario for multiple challengers would be if you had one representing the "RINOs" (probably Kasich) and another representing either the "true conservatives" or "libertarians" (possibly Amash?).  But even coming from different wings of the party, they would still probably dilute the anti-Trump vote if they were both in the race at once.