The Real Clear Politics Electoral College Map currently has the Obama/Biden ticket with 210 electoral votes and the Romney/Ryan ticket with 181. There are 12 “toss up” states with 156 electoral votes. If the toss up states are given to the slate to which they are currently leaning, Obama/Biden has 294 electoral votes and Romney/Ryan 244.
However, if just three of the closest toss up states (Virginia, Iowa and Nevada) were to switch to the Romney/Ryan camp, it would result in a deadlocked electoral college, with each ticket having 269 electoral votes.
Supposing that were to actually occur, what would happen? Under the Twelfth Amendment, if no person receives a majority of the electoral vote for President, “then from the persons having received the highest numbers not exceeding three on the list of those voted for as President, the House of Representatives shall choose immediately, by ballot, the President.” Presumably that list would consist only of President Obama and Governor Romney, although note that any one elector could expand the list by voting for someone else.
The choice of the President would be made by the 113th Congress so we do not know what the exact partisan breakdown of the newly elected House will be. However, the voting for the presidency would be by state, not by individual member, and, as this CNN article suggests, it is highly likely that the Republicans will control a majority of the state delegations, even if the Democrats win back control of the House. Thus, it seems that Governor Romney would be the heavy favorite.
If no person receives a majority of the electoral vote for Vice-President, the Twelfth Amendment provides that “then from the two highest numbers on the list, the Senate shall choose the Vice-President; a quorum for the purpose shall consist of two-thirds of the whole number of Senators, and a majority of the whole number shall be necessary to a choice.” We do not know who will control the Senate in the next Congress, although the Democrats appear to be the favorites at this point. Thus, the odds suggest that Vice-President Biden would be elected by the Senate.
But what happens if there is a 50-50 tie in the Senate? Could Vice-President Biden vote to break the tie in his own favor? This article says yes, but I am not so sure. One could argue, it seems to me, that the “majority of the whole number” refers to the whole number of Senators, and that the Vice-President’s vote cannot create a majority of that number. There would also be, I imagine, objections raised to the Vice-President voting in his own election. So we can consider that an open issue for the moment.
Update: Writing in the Washington Examiner, Philip Klein also suggests that Biden could cast a tie-breaking vote for himself. However, the more I think about this, the more I tend to think it is wrong. Suppose 50 Democratic Senators vote for Biden, but one or more Republican Senators did not vote, so that Ryan receives 49 or fewer votes. Biden would not be able to vote because the Senate would not be “equally divided,” but no one would be elected because the winner must receive the votes of a majority of the whole number (ie, 51).
Note the additional complication that could occur if a Senate seat were vacant as of January 3, 2013 (because, say, the election was contested and the state had not yet certified a winner). In that case there would be a question whether the “whole number” referred to by the 12th Amendment is 100 or only the total number of Senators seated and sworn (i.e., 99).