If the results of the Electoral College’s vote for President are tied, the vote goes to the House of Representatives. The House can vote on the top three Electoral College vote-getters. Each state gets one vote; the votes count equally. It’s the newly-elected House, not the outgoing lame duck House, that would meet to vote.
We may safely presume that no Representative would be absent from the House on that day, and that they would vote with their parties without fail. The reprecussions for voting against one’s party in a disputed election for President would be enormous.
Based on the current House membership, a straight party-line vote would be 27 votes for Obama, 21 votes for McCain, and two delegations (Arizona and Kansas) equally split and therefore not voting. However, within that breakdown, there are twenty states that would decide their vote by a single vote within the delegation — ten for each party. Some of these are because the states are so small there is only one Representative from each state, others because those states are tightly-divided and control of the delegation would be up for grabs in a single contested district.
For the Republicans, these are Alaska, Delaware, Georgia, Louisiana, Missouri, Montana, Nevada, New Mexico, Utah, and Wyoming. Of these, Delaware and Wyoming are not realistic candidates for a split. Alaska normally would not be, either, but its Congressman is likely to be tainted by the Ted Stevens corruption scandal. For the Democrats, those are Colorado, Indiana, Iowa, New Jersey, North Carolina, North Dakota, South Dakota, Tennessee, Vermont, and West Virginia. Of these, only Vermont is a lock to stay Democratic. So it is not hard to imagine several of these states flipping control. And Kansas and Arizona are potentially up for grabs if a district changes in those states, which again is not out of the realm of possibility.
Turnover in the House is low. Of the 435 seats, 31 changed partisan control in the momentus 2006 election. That’s a 7% shift. By comparison, in 2004, only 4 seats changed partisan control, for a rate of less than 1%, and in 2002, only 8 seats changed control. But one party almost always sees a net gain in an election. Given that 19 out of the 50 states are at least questionable in terms of which party controls a delegation, it is not a foregone conclusion that Obama would win if the election results in a 269-269 tie. Obama certainly has an advantage in that forum, but not a lock.