Ezra Klein believes that the White House wants to drive a stake through Mitt Romney's candidacy so that the party nominates a more radical (and unelectable) figure. Here is an example of an instance where liberal interests diverge from the Obama administration's interests. From Obama's perspective, the crazier the Republican nominee, the better. Better Tim Pawlenty than Mitt Romney, and better Sarah Palin than Tim Pawlenty.
The broader liberal calculation is different. It's almost certainly true that liberals will want Obama to win reelection. But we have to balance that desire against minimizing the downside in case he doesn't. And if unemployment or other conditions are sufficiently dire, even a Palin could win the nomination. So at that point, the difference between regular Republican-bad like Romney -- which, don't get me wrong, is pretty bad -- and Sarah Palin-bad is pretty significant. Accepting that risk in return for a somewhat higher chance of Obama getting reelected is a risk the administration would happily take, but I wouldn't.