It's hard to know what conflicted voters will do.

But there is what I will call the Danforth effect. Former GOP Senator (Mo.) and UN Ambassador John Danforth was interviewed after his old colleague Richard Lugar was defeated in the primary by an Indiana Tea Party Republican. He said:

THINKPROGRESS: What do you think is happening here?


DANFORTH: An effort by some, and apparently a large number, 60% in Indiana, to purge the Republican Party and to create something that’s ideologically pure and intolerant of anybody who does not agree with them — not just on general principles, but right across the board.


THINKPROGRESS: Do you stand by your view that GOP is beyond hope?


DANFORTH: If this trend succeeds, yeah. What they will be left with, if indeed they want to purge the party of all but people who have a particular ideological slant… it’s not a way to win elections, it’s not political[ly] sustainable. It might make them feel good for a time but doesn’t work, it hasn’t worked. It didn’t work in Nevada or in Delaware in last election. They won nominations but couldn’t win elections. I don’t know how you win elections without getting 51% of the vote. I don’t see how you’re gonna get 51% of the vote if you make it clear that people in your own party, who don’t absolutely agree with everything you want to do, aren’t wanted.

[Bolding mine]
If Danforth is right, the new GOP purists will turn off the independents; they will turn to Obama; and the GOP will have lost its brand as well as the election. He may not be correct, but he's a very savvy politician whose views should not be summarily dismissed.