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John Kerry and the prospect of an empty MA Senate seat

J. Scott Applewhite / AP, file

John Kerry is pursued by reporters as he arrives for a closed-door meeting about the assault on the American consulate in Benghazi, Libya, on Capitol Hill on Nov. 13.

The second-term cabinet intrigue continues.

Although U.N. Ambassador Susan Rice remains the front-runner to be President Obama's next secretary of state, Sen. John Kerry (D-Mass.) is still in contention for the post.

And if Rice gets that coveted job, it's assumed that Kerry might become the next defense secretary.

But Kerry getting either position presents one potential downside for Democrats: His exit from the Senate would trigger a special election in Massachusetts, with recently defeated Republican Scott Brown waiting in the wings to possibly mount a comeback.

That prospect could very well explain why Senate Republicans have showered praise on Kerry after all the controversy surrounding Rice's initial statements about the attack on the U.S. consulate in Benghazi.

On Wednesday, Sen. Susan Collins (R-Maine) -- who told reporters about her concerns about Rice after meeting with the U.N. ambassador -- offered that Kerry would be "an excellent appointment."

Brown even recommended Kerry for the secretary of state job at a Nov. 13 press conference in response to a question about whether Kerry would make a good defense secretary. “I’ve already been public on that quite a while ago. And I’ve told him personally that I thought he would make an excellent secretary of state. I haven’t even thought about any other positions but those are questions best asked of him and the president.”

But the running theory that Republicans want Kerry as secretary of state to so they can win his Senate seat ignores two realities.

One, that Senate seat is likely to be vacant whether or not Kerry gets the secretary of state job -- because he would be in line for the defense job.

Sen. Kelly Ayotte (R-N.H.), one of Rice's chief critics, said it was "absurd" to think that Republicans are opposing Rice to open up Kerry's Senate seat. "I would remind you this is an issue that I was pursuing and others long before the election, before we knew whether Scott Brown was going to win that election. So I think that claim is absurd.”

And two, Brown or any other Republican wouldn't have an easy time winning in a special election. "We don't think another Senate run is going to play differently for him," said Matt Canter, communications director of the Democratic Senatorial Campaign Committee.

"He lost by eight points. It was not a close race." Democrat Elizabeth Warren beat Brown, 54%-46%.

And a plugged-in Massachusetts Democrat tells First Read, "The reality is, Scott Brown's only a Goliath in the eyes of Beltway liberals still scarred by his special election win two years ago," adding: "His brand is badly damaged in Massachusetts, even if his legend lives on in Washington."

But a Kerry vacancy would give Brown or any other Republican a chance -- which is a better prospect that they have now.

As one GOP operative emails, “I’d certainly like to see that vacancy, and I’d like to see Scott run.”

*** UPDATE *** Also according to the exit polls, 60% of Massachusetts voters on Election Day had a favorable opinion of Brown (versus 56% who said the same about Warren).

NBC's Tom Curry contributed to this article.