Molly Ball's profile of Harry Reid explaining how he ended up with Sharron Angle as a general election opponent explains why I don't think he's going to face a leadership challenge:
In fact, luck had very little to do with it. But Reid had everything to do with it. He spent years clearing the field by enticing, bullying, and manipulating the strong potential Republican candidates into opting out. The dean of the Nevada political press corps, television host and columnist Jon Ralston, frequently refers to Reid as the state's "Meddler-in-Chief," because nearly everything that happens in the Silver State bears his fingerprints.
Nowhere has that been more evident than in the race to run against him. It belies the common perception of him as a bumbling, mush-mouthed, accidental leader. By reputation, he is no Lyndon B. Johnson or even Rahm Emanuel: The Washington Post's David Broder called him "a continuing embarrassment thanks to his amateurish performance" as majority leader. But the way he's engineered his current electoral situation shows that Harry Reid is no less a master of the inside game.
Reid is a woefully ineffective public voice for the Democratic Party: He's bad at leveraging public opinion against the opposition, he's not very good at articulating progressive values. He is, however, great at herding cats and at manipulating things behind the scenes. Yesterday's win was basically the last shot in a slow-motion political reproduction of the final scene in The Godfather, with Reid as Corleone. Or as Sen. Chuck Schumer, one of Reid's prospective challengers put it, Reid will "kneecap you if you cross him." Coming back from the dead yesterday reminded anyone with leadership ambitions why crossing Reid wouldn't be a good idea.