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12th Amendment Update: Tie Probability Continues to Increase

The latest in our occasional series informing you about the country’s worst nightmare: a 269-269 Electoral College tie…

As you may have noticed from our scenario chart, the probability of a tie has increased dramatically in recent days and now stands at 3.2 percent. This is partly because, as we draw closer to election day with the race remaining tight, the probability of any one candidate running away with the election diminishes — meaning that all “close” electoral permutations, including ties, become more likely.

However, there is one specific scenario that is driving this outcome. That is the scenario wherein Barack Obama wins the Kerry states plus Iowa, New Mexico and Colorado, but loses New Hampshire. Of the 320 times that our simulation ended in a tie, this particular scenario was responsible 294 times. Indeed, we presently have Obama winning precisely the Kerry states plus Iowa, New Mexico and Colorado, so all that would be needed to make a tie occur is to flip New Hampshire back to McCain, and entirely reasonable possibility.

Four other 269-269 tie permutations came up with less frequency:

20 times: Obama wins Kerry States + IA + NM + NV. This once had seemed like the most plausible tie scenario, but it requires Obama to win Nevada while losing Colorado, and increasingly unlikely parlay.

3 Times: Obama wins Kerry States + IA + NM + WV. Functionally equivalent to the scenario above since West Virginia and Nevada each have 5 electoral votes.

2 Times: Obama wins Kerry States + IA + NM + CO + VA – MI. Michigan has moved slightly toward Obama in the post-convention polling while Virginia has remained stuck in place, making it less likely that the states would invert positions as this scenario requires.

1 Time: Obama Wins Kerry States + IA + NV + CO – NH. Obama winning Nevada while losing New Mexico now seems very unlikely.

By the way — the way that the tipping point math works out, about 80 percent of the tie outcomes involve McCain winning the popular vote. This is by far the messier of the two scenarios. Since the Democrats will almost certainly control a plurality or a majority of House delegations in the incoming Congress, a tie accompanied by an Obama win in the popular vote will lead to a lot of fanfare but ultimately little drama — Obama will become the next President. But if McCain wins the popular vote, there will be far more pressure on Democratic Representatives to vote against their party. I still tend to think that this scenario favors Obama (formally, our model splits them 50:50) but a whole number of factors come into play, including:

(i) The size of the Democratic edge in House delegations;
(ii) The magnitude of McCain’s popular vote margin;
(iii) Whether any states have their outcome determined by recounts. For instance, if Obama loses a controversial recount in Virginia by a few thousand votes and this produces a 269-269 tie, Representatives will have a far easier time finding it “fair” to vote for him than if the reverse were to occur.
(iv) The overall tenor of the campaign from here forward.

Nate Silver is the founder and editor in chief of FiveThirtyEight.