A fine idea, fraught with political peril.

In defiance of traditional party labels, Barack Obama, the Democratic presidential nominee, may ask the defence secretary of President George W Bush to stay on if he wins the White House.

Obama’s top foreign policy and national security advisers are pressing the case for keeping Robert Gates at the Pentagon after he won widespread praise for his performance. The move would be in keeping with Obama’s desire to appoint a cabinet of all the talents…

Richard Danzig, an adviser to Obama on national security and a former navy secretary, said: “My personal position is Gates is a very good secretary of defence and would be an even better one in an Obama administration.”…

Gates recently said Obama and John McCain, his Republican rival, were likely to take a “sensible approach” to Iraq because “the next president would suffer the greatest consequences if we do get the endgame wrong”. Retaining Gates would give Obama “cover” for adjusting his policy if necessary, while reassuring Republicans that withdrawing from Iraq would not imperil national security.

I remember some lefty blogger arguing a week or two ago when this first popped up that the Dems can’t afford to have a Republican at the top of the chain of command lest it reinforce the impression that only conservatives can be trusted with war. Fair point, except of course that it’s not war that’s on Obama’s agenda; it’s withdrawal, and per the boldfaced part, having a prominent Republican in charge of it would actually help undo the perception that the left alone is responsible for retreat. Lefty blogger Spencer Ackerman made the same argument a few months ago about why they should welcome Petraeus’s promotion to Centcom commander — not because it’d improve our chances of winning in the Middle East, but because having someone at the reins who’s held in esteem by the right would be useful as political cover when the great drawdown begins. As such, the question is whether Gates, knowing what Obama has in mind, should refuse to stay on to avoid being turned into a political prop. I say no: If he thinks he can do some good, even with a task as unseemly as that, it’s reason enough to continue. He wouldn’t have to stay long, either. Clinton had three Defense Secretaries in his two terms (one a Republican), and no doubt Obama would want Gates replaced with a Dem at some point after withdrawal begins or even ends to address the concern articulated by the lefty blogger. Exit question: Should he stay if asked, and should Obama ask him?