SENATORS WHO MOVE TO THE CABINET…. Much has been made of the fact that sitting senators have very rarely won the presidency. Barack Obama is the first since JFK 48 years ago, and only the third in American history, following Kennedy and Warren Harding.

But what about senators becoming cabinet secretaries? Ben Smith had an interesting item this afternoon.

Along with getting emoluments out of the way, Lloyd Bentsen offers a useful guide on another timely question: When will Hillary resign?

Her staff isn’t saying, but Bentsen is the most recent sitting senator to join the cabinet, and a likely guide. The Senate Finance committee met and voted the nomination out on January 12. Clinton was sworn in on January 20, and the Senate briefly convened hours later to hear Bentsen’s nomination, along with those of Les Aspin and Warren Christopher.

Only then did Bentsen resign.

Which means nearly two more months of obsessing about David Paterson.

Sure, there’s going to be ample speculation about who’ll fill Clinton’s Senate seat. But let’s not brush past that first point — we haven’t had any sitting senators move to the cabinet since Lloyd Bentsen? That was 15 years ago, meaning Clinton didn’t call on any sitting senators to fill cabinet vacancies after his first year in office, and George W. Bush didn’t call on any at any point during his two terms.

I wonder why this is. Part of it, I suspect, is that being a U.S. Senator is a great gig, the job security is generally pretty good, and one would ordinarily be reluctant to give it up for a cabinet post that only lasts a few years.

But I’m still surprised we’ve seen zero senators move to the cabinet over the last 15 years. There are some pretty talented officials in the chamber; why overlook them?

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.