Let's jump to early August ...

[Mr. Morden]

Of course Portman wouldn't automatically become the nominee since Romney naming him as his running mate has no official meaning.  All that means is that he's asked his delegates to vote for the nomination of Portman as VP.  But that nomination vote doesn't happen until the convention.

I presume that all of the uncommitted and unpledged delegates would still be able to vote for whoever they want, and any delegates awarded to Gingrich or Santorum or whoever else would be free to vote for whoever they want *if* Gingrich or Santorum has released their delegates by that point.

Presumably, the delegates pledged to Romney would not be bound to vote for his nomination anymore if he's dead.  I guess anyone, whether they ran this year or not, would be fair game for winning the nomination.

Btw, Intrade gives Huckabee a 0.4% chance of winning the nomination, while Jeb Bush is given a 0.3% chance.  That puts them ahead of everyone but Romney and Paul.

[Mr. Morden]

Do the rules that bind convention delegates to a particular candidate on the first ballot actually envision a scenario in which the candidate dies before the vote, or would most of the Romney delegates technically be bound to vote for him on the first ballot even if he's dead?

Also, presumably the rules are the same on the Democratic side?  If something happens to Obama before the convention, then the delegates can vote for whoever they want, but if it's afterwards, then the DNC picks the replacement?

And at what stage would it no longer be the DNC or RNC picking the replacement, but rather the individual electors?  Does that only come into play if something happens to the candidate after the election but before the electors meet?