In a surprise move, the House Democratic Caucus has stripped its longest-serving member of a top committee post in favor of a more liberal challenger. California Rep. Henry Waxman topped Michigan Rep. John Dingell by a 137-122 vote in the battle over the House Energy and Commerce Committee, according to a top Democratic aide.

Dingell, the dean of the House and the second-longest serving member in Congressional history, lost his post after nearly three decades as either the chairman or the committee's ranking member. Dingell had sparred recently with House Speaker Nancy Pelosi over global warming and auto industry issues.

Waxman, the committee's second-ranking Democrat, chairs the House Oversight and Government Reform Committee and is seen as more liberal. He is an ally of Pelosi's, and many suggested the Speaker played a role in the surprise challenge, especially as top lieutenant George Miller whipped votes on Waxman's behalf. Pelosi aides have denied any involvement and expressed as much surprise at the challenge as anyone.

It's the second round of voting in two days in which Waxman has emerged on top. The Democratic Steering and Policy Committee voted by a 25-22 margin for Waxman on Wednesday, though some suggested that because that body is largely loyal to Pelosi and regionally tilted toward the West, Dingell would be in better position to win a vote amongst the full caucus.

Update: Politics Nation is told Iowa Rep. Bruce Braley, just elected to his second term, made an impassioned speech on Waxman's behalf, blaming Dingell for blocking progress on a number of bills. Braley has been involved in the Democratic Congressional Campaign Committee, co-chairing the Frontline program, but it's still unusual to see such a junior member of congress question a more senior member, especially one who was serving his second term in Congress when Braley was born.