Contested convention: Can delegates choose a non-candidate?

Straight-forward question about nominating conventions:

If the convention ends up contested, and the delegates are freed of their pledges, can they nominate someone who wasn’t a candidate (like Romney or Arpaio :eek:) ? Or are they constrained to choose among the candidates still running? Or including former candidates whose campaigns were “suspended” (like Jeb! or Walker)? Does each party make their own rules about such things?

I may well be wrong here, but my understanding is that if a nomination doesn’t happen on the first ballot, it’s anybody’s game.

I’ve heard this explanation before. I’ve also heard the explanation that the only candidates eligible after the first vote are candidates that have won at least eight states. I’m not sure which of those is correct. I’m also not sure that Rubio, Kasich, or even Cruz with the four states he already has will manage to achieve victory in eight different states.

The only part of this I can answer is this, yes the main parties have their own rules governing the nominating process and they differ in important areas.

You need eight states for the first ballot, not after that.

So, there’s still a real possibility that the nominee could be someone like Jeb, or Mitt, or Paul Ryan, right?

(It’d piss off and alienate all of the people lining up to vote for Trump, of course).

It depends on how close Trump is. Say Trump fails on the first ballot, but he has 45% of the delegates he needs. On the 2nd vote, they just have to get a small number of delegates to vote Trump.

Also, how pissed Trump voters are and how much it matters depends on how many he won. If he only wins a third of GOP voters, which is what he’s on pace to do now, screw 'em. You’re entitled to nothing, getting a third of the vote. But most Trump voters I’ve talked to do like some of the other Republicans. The main issue is that some Trump voters are disaffected voters who otherwise won’t come out in November, as well as some Democrats. Who also won’t have a place to go since Sanders lost. But losing them is better than losing the broad middle, so again, screw 'em.

So of Rubio only wins seven states, what do his delegates do?

This seems to be the Conventional Wisdom, but skimming the GOP rules, I’m not sure its true, at least under the current rules. I think they can change the rules during the convention, so maybe that’s what people mean.

Here’s the full text of Rule #40, which seems the relveant bit.

ETA: For all the coverage of the election, there’s surprisingly little attempts to break down what would actually happen at a contested convention. I figured some of the more wonky sites like vox or fivethirtyeight would’ve tried to play-out the rules so the rest of us don’t have to. But I guess the possibility is still remote enough that even people that do that kind of thing for a living haven’t been able to stomach having to actually parse the GOP convention rules in detail.

All that means is that for the 2nd ballot, 8 states have to agree on a nominee to put his name in nomination.