I had better start with the main point here, since I’m going to backfill a bit to get to it: Parties matter more than individual candidates.

First, some context.

There has been some interesting discussion of the Iraq War and the Republican Party in recent days; I linked to Daniel Larison’s comments earlier, and today Conor Friedersdorf responded by pointing out that several Democratic presidential contenders, including Hillary Clinton, voted for the Iraq war resolution, and that such votes could be a problem:

It's conceivable that someone like Rand Paul will win the GOP nomination, and the general election will feature a Republican nominee attacking his Democratic opponent's war support in much the same way that Obama successfully attacked Clinton: "You thought the Iraq War was a prudent invasion, and now you want to be president?"

Later, on Twitter, Friedersdorf suggested it depends on who the nominee is.

Thinking about it that way, however, puts far too much emphasis on the nominee and too little on the party. As far as I can tell (and as Larison lamented) most Republican Party actors, especially those who care about foreign policy and national security, remain supporters of at least the original rational for the war. If that’s correct, then the nominee, whoever it is, will wind up adopting the party position. Similarly, if a candidate isn’t willing to adopt it, he or she won’t get the nomination.

Nomination battles are where parties resolve their identities. It’s always possible that Republicans in 2016 will be a different party than they were in 2004 of 2008 of 2012 or, for that matter, right now. On the other hand, it seems unlikely to me that Iraq is a fight that Rand Paul or anyone else would choose; if dissenters want to change the Republican position, why pick a decade-old issue on which many in the party long ago dug in?

What matters is what the Republican Party believes, not what its nominee believes -- because the former will constrain the latter. Especially for policy positions on which party actors feel strongly. It’s the party, not the candidate.