For most of the reasons cited by Dylan, liberals should be unahppy if Obama choses Tim Kaine as his running mate. Still, I can least imagine an argument on his behalf: He could win Virginia for the Dems, a major blow to McCain, and his more conservative positions are unlikely to affect the way Obama governs. I reject the argument because I don't think there's good evidence that Vice Presidential nominees have a significant positive influence on voting behavior, so running mates should be primarily be chosen on the merits (on which Sebelius is clearly preferable to Kaine.) But I could at least find this argument intelligible.
Micheal Sean Winters, on the other hand, seems to argue that Kaine's reactionary positions on reproductive freedom are a feature, not a bug. His argument is rife with the kind of illogic endemic to claims that the path to Democratic victory is selling out women. Most importantly, it's far from clear how many potential Democratic voters will be affected by critiques of Sebelius from a priest "who has been published in the conservative Catholic journal First Things, a magazine that often mimics White House talking points more faithfully than it follows the teachings of the Catholic Church." But since these attacks on Sebelius for being pro-choice didn't stop her from being elected in one of the most conservative states in the country, it's hard to imagine they could significantly impact a national race, and Winters provides no evidence otherwise.
Even more importantly, while implying that Democrats should choose Kaine over Sebelius to chase voters unlikely to vote for the Dems in any case, he completely ignores the costs of such a strategy. Democrats also need votes, donations, and activism from their pro-choice base, who would be (properly) dismayed by a selection of Kaine. And given Obama's path to the Democtratic nomination, this seems like an especially bad year to stick a thumb in the eye of women and effectively declare reproductive freedom a second-class issue. Once you consider the potential costs alongside the (highly dubious) benefits, the argument for Kaine cannot be sustained.
There are other reasonable choices, but if it comes down to the two red-state governors, Sebelius is far and away the better choice for Obama.
--Scott Lemieux