DeMint probably supported Mitt for the same reason I voted for Mitt in the Michigan primary: he wasn't John McCain.
By the way quietcontrarian: In the Michigan primary, Mitt was big on federal support for the “Detroit Three.” Whatever you think the voters want to hear, that's Mitt.
I actually had to go look back because I'm not sure of what he specifically said back in MI. From what it looks like, he suggested he would aid the companies with their healthcare/pension costs (though not clear what aid means - and would it require bankruptcy) and would either help the companies with research to get to mileage requirements or eliminate the requirements.
I can't really call that a flip flop.