(1) A Centrist-Left candidate who, while many hope he will move to the Right, is already moving to the Left and "Me tooing" Obama. One who will likely neuter any Conservative gains in the House and Senate and crash the country as bad, giving Conservatives a bad name as well.
(2) I'll give you this one.
(3) Supporting the GOP Leftist so that the future will hold candidates further to the Left for both parties.
The same logic the "Never McCain" conservatives used in 2008 - and look how 'right' our current candidate is and how wonderful 0bama worked out for us. So let's do that AGAIN because it worked so well the last time! (!)
Conservatism isn't about being so rigid we break - in this case it's about doing what's best for the country with what we have. A hope for a better candidate in 2016 isn't a 'have', it's a hope. There is NO EXCUSE for a conservative-libertarian to directly or indirectly assist 0bama's reelection.
I have seen the enemy ... and it looks a lot like us.