Elizabeth Warren, the U.S. Senate candidate from Massachusetts, announced on Twitter yesterday that she got a good-luck call from President Obama aboard Air Force One. A nice gesture from a person in a nail-biter of a race of his own. But another gray-beard Democrat might not be so keen on a Warren win. I’m talking about the senior senator from the Bay State, John Kerry.

Everyone knows that Kerry, the chairman of the Senate Foreign Relations Committee, wants to be secretary of state. Yet he needs Obama to win and Warren to lose tomorrow night to have a chance at securing the coveted top spot at Foggy Bottom.

(Steven Senne/Associated Press)

The Democratic majority in the Senate, where it takes 60 votes to do anything of late, is slim. There are 51 Democrats, and two independents who caucus with them. It could be slimmer still in the new Congress after Tuesday’s voting. Still, plucking Kerry from the Senate would reduce that majority further.

If Kerry were to become secretary of state — again, assuming Obama wins — Gov. Deval Patrick (D) would appoint someone to fill the vacancy until a special election were held between 145 days and 160 days of the seat being vacated. The messiness of all this is rich with irony. Were Warren to lose to Sen. Scott Brown (R), a Kerry departure to the State Department would make her a shoo-in to replace him — thus, not disturbing the Democrats’ delicate balance in the Senate.

Before Sen. Ted Kennedy died in 2009, he got Patrick to agree that the person selected to fill his seat until the special election would not run. The governor is not bound by law to follow that precedent. If I were Warren, I’d insist on being able to run while serving as the appointed senator. After the race she’s run, she’d be well within her right to make such a demand. And Warren would win.

The latest poll from the University of Massachusetts-Lowell and the Boston Herald released this morning shows Brown leading by one point — essentially a tied race. But a Warren win tomorrow night could spell trouble for Kerry. With all the tough votes ahead, would a reelected Obama want to diminish his party’s hold on the Senate by installing Kerry at State? A Kerry departure would make it possible for a defeated Brown to run for and win Kerry’s vacated seat, thereby giving the Republicans a seat, if not a reliable vote.

The Boston Globe’s Glen Johnson explored the Brown-replaces-Kerry possibility last month. Johnson calls this Brown’s “fallback plan” if he loses to Warren. It makes sense. But it requires Obama to win and Warren to win. And I’m not sure the president or Senate Majority Leader Harry Reid (D-Nev.) would put the razor-thin Democratic majority at risk to fulfill Kerry’s ambition.