(Associated Press)

Warren is a particularly tough challenger for Brown. His initial election was the product of some very rare factors: First, it was a special election. Second, his opponent, Martha Coakley, was joyless, gaffe-prone, politics-as-usual candidate at a moment when people really hated not only politics-as-usual, but politics-at-all. Forget winning independents. Even Democrats didn’t like her. Third, the tea party was at peak levels of excitement, while Democrats were increasingly disillusioned.

Warren turns most of that back on Brown. The next election is a presidential election, which means that Obama will be on top of the ticket and Massachusetts Democrats are going to have a long campaign in which to remember how they feel about Republicans. Brown is now a senator, with gaffes and goofs of his own, while Warren is an outsider who fought the administration over TARP and is waging a seemingly doomed battle to keep banks and credit-card companies from screwing average Americans over. Third, the tea party likes Brown less than they used to — in fact, some members have turned on him outright — and Democrats in general and liberals in particular adore Warren. It’s very likely that the balance of enthusiasm would be on her side, not his. And though Brown’s poll numbers are high, the state’s political observers consider his support soft. A Warren win atop Obama’s coattails is a lot likelier than, say, Scott Brown winning in the 2010 special election.

The obvious deal seemed to go like this: Brown convinces Mitch McConnell that it’s better to have Warren running the CFPB than replacing a Republican Senator with a Democratic one. But Republicans seem more interested in hamstringing the CFPB than protecting their own. So though Warren’s Washington fans are probably feeling pretty down right now, I have a hunch that her Massachusetts admirers are getting excited.