Really bad idea.
Or is it? I'm wondering if Obama ought to consider it. What better incentive to centrists than to put a Republican with a lifetime American Conservative Union Rating of 86 on a Democratic-led ticket? If Iraq is going to be front and center, then Hagel is uniquely positioned to help Obama push a new consensus about ending the Iraq occupation as another element of Obama's post-partisan philosophy. This is all not to mention that Hagel, unlike his old pal McCain, really is an expert on the military and foreign affairs (no matter how often McCain touts his expertise, his statements on Iraq tend to contradict each other daily), but because of the unique properties of such a ticket, it might be possible for Hagel to add some experience, etc., to the ticket while the meme about how he reinforces Obama's lack of experience on these issues gets lost in the shuffle. Or something like that.
Considering how poorly Hagel has been treated by his party, I'm guessing he'd be willing to do it. Some might say that Hagel parallels Lieberman, although I'm not sure that fits entirely--Lieberman, after all, did retain some supporters in the Democratic Party, and there is certainly still a hawkish wing of the party, even though the differences have been smoothed over somewhat in the past few years. Hagel was effectively thrown to the wolves. And the transition from Joe Lieberman running for the opportunity to run against Bush in 2004 to his (literal) embrace of the man--and right-wing anti-anti-Bush talking points--within such a short time was just bizarre. And Lieberman was always iffy on a lot of issues. He's a quintessential New Democrat, which in my experience tends to mean a voting record much like a Republican's, but with a 100% NARAL rating. Not that the latter is necessarily a bad thing in and of itself, but I'm glad that being liberal no longer just means "pro-choice".
Of course, while the benefits of Obama/Hagel are large, the risks are also large. Obama might very well manage to alienate, well, every shade of Democrat there is with such a move. Hagel is a conservative in pretty much every way except foreign policy (and, I suppose, immigration), and everyone from unions to pro-choice groups aren't going to be nuts about the idea of him just a single heartbeat away from the presidency. And they'd be right not to want that to happen. Then, there is the reality of Hagel's less-than-shining performance in the past few months--he's so passionately against the war that he's
Of course, Obama/Hagel would probably necessitate a McCain/Lieberman ticket, lest McCain fear being one-upped. Then Michael Bloomberg, who has finally, for the next time, said he's not running for president, changes his mind and picks Sam Waterston as a running mate. Then all hell breaks loose...