It is almost beyond comprehension and could cause a constitutional crisis like we've never seen.
In the case of a 269-269 tie in the Electoral College, we could we end up with—brace yourself—President Romney and Vice President Biden. This is a scenario that, although dreaded by most, is becoming more plausible in a race where the polls are virtually tied.
The 12th Amendment to the U.S. Constitution spells out how it would work.
If the Electoral College is tied, then the House of Representatives votes for the president, with each state delegation getting one vote. Republicans have the majority in twice as many delegations as the Democrats. Even if the House were to go Democratic, it's likely that Republicans would retain control of many of the states' delegations. So Romney becomes President.
On the Senate side, each Senator gets one vote for vice president. Democrats currently have control of the Senate with 51 Democrats, 47 Republicans and two independents: Bernie Sanders and Joe Lieberman. If Democrats keep control of the Senate, then Vice President Biden is the likely winner. And if the Senate goes 50-50, the Constitution calls for the Vice President to cast the deciding vote. Presumably, Vice President Biden would vote for himself and remain VP.
Recently, NBC News Political Director Chuck Todd, host of msnbc's The Daily Rundown, broke down how all of this could play out should the electoral end up in a tie.