Steve Benen enters a guess in the sweepstakes (or at least notes Roll Call's guess):
But let's say Republicans come up short and win, say, 35 seats. Under normal circumstances, that would be a pretty good cycle for a discredited party that most the country neither likes nor trusts, but given GOP expectations about massive gains this year, failing to win a House majority would be a pretty devastating setback.
As it turns out, though, even if Republicans fell short of a +39 cycle, they wouldn't necessarily wait until 2012 before trying to get that majority. Indeed, if the GOP came up a few seats shy of 218, they'd just try to flip some Blue Dogs.
It's happened before. Or at least, party switching has happened before. The last major shakeup, though, was in 1994-95, after Republicans actually succeeded in taking over the House in their own right. Falling short and looking to pick up a few votes and collapse across the finish line is perhaps a different story.
And just to add a twist, I wonder whether House Republicans really want it. There's a good argument for why Republicans might do best politically by falling just short of enough seats to actually have to govern. There's certainly no indication from their campaign "pledge" document that they've got anything concrete in mind, anyhow, so they might do just as well to play the frustrated minority in what they'll portray as an evenly-divided country, in the hopes of making a credible bid for the White House in 2012.
After all, in truth, Republicans don't believe much in the power of the legislative branch. That, too, is evidenced by their lack of specificity in their pledge. They're pretty solidly dedicated to executive primacy, especially when they hold the executive. Recall that in the 40+ years since electing Nixon (whose executive primacy doctrine it is they still adhere to), Republicans have held the White House more than twice the amount of time as have Democrats.
Even when they don't hold the White House, they still believe in a kind of executive primacy, which is why it's so very important to them to spend their energy as legislators not legislating, but working to undermine the legitimacy of any Democratic executive. It's more important that people have doubts about Bill Clinton's finances or personal life, or Barack Obama's birth or religion, than that they actually promulgate policy ideas. No matter who wins the White House, most Republican legislators put all their focus on the executive branch: rubber stamping it as a Politburo when the President is a Republican, and opposing and undermining it when the President is a Democrat. Even when the President is a Democrat who proposes adopting what were once Republican ideas.
None of that is to say that Republicans wouldn't be pleased to have control of the House handed to them. Certainly John Boehner would like nothing better than to have the trappings of higher office available to him, which he might comfort himself as he's forced out the door by the up-and-comers who consider him something of a ridiculous and useless holdover from a Republican era gone by. But given that they clearly have no plan for what to do with a majority (besides issue subpoenas aimed at exactly what I told you they aimed at, above), I don't know how aggressively they'll pursue it.
Besides which, any Blue Dog who survives this year is likely to be pretty well convinced of his own formula for success. And you couldn't fault them much for thinking it had something to do with being able to demonstrate a kind of independence from the Washington leadership of both parties. It seems much more likely to me that they'll see being part of a narrow majority of Democrats as much more valuable in terms of leverage than being part of a narrow majority of Republicans. Luring them into the GOP fold will most likely mean offering them leadership positions, which puts them on the spot for voting the leadership line. That's not how they convinced swing districts to vote for them, and it's not how they've built the leverage they've enjoyed as Blue Dogs. Their power comes from being able to be the last holdouts on every vote. Becoming Republican leaders, responsible for advancing a party line, would mean largely surrendering that power.
Could it happen? Absolutely. A Blue Dog Democrat who's decided he's had enough of the constant struggle of walking the electoral tightrope might well be convinced to cross the line in exchange for two last years of relative comfort, followed by retirement (or the leap to K Street). But I think there are lot of other forces acting on the decision besides the simple numbers of majority making.