Election 2012 - How Overland Park, KS cost Romney the presidency

How did one of the following places win the 2012 election for Barack Obama and cost Mitt Romney the presidency?

Overland Park, Kansas, or
Rancho Cucamonga, California, or
Fort Lauderdale, Florida, or
Tuscaloosa County, Alabama

And, why these places?

While the presidential election of 2012 is behind us now, it is worth looking at the less-than-obvious math behind what it takes to win. First, let’s look at the reported numbers.

Electoral college results: Obama 332, Romney 206.
Popular vote:  Obama 65,910,437, Romney 60,932,795.  A difference of 4,977,642 votes.
Popular vote: Obama 51.07%, Romney 47.21%.  A 3.86% margin of victory.

The Electoral College results suggest that Barack Obama won by a wide margin, and even the popular vote totals would suggest a comfortable victory. But is that really true?

What was the real margin of victory? Turns out it was about 166,500 votes or 0.136%.  That is a much thinner margin than the ones above. Where did 0.136% come from?

The secret to winning is to collect enough Electoral College (EC) votes. Doing that requires carrying enough states to reach 270 EC votes. By analyzing the states with the smallest margins of victory for Barack Obama, then prioritizing them according to their electoral votes, it is possible to calculate how many voters in each state had to switch from Obama to Romney to give that state’s EC votes to Romney. Romney needed to get 64 more EC votes (206 + 64 = 270).  This would simultaneously remove them from Obama’s total (332 - 64 = 268).

Here’s the math. (numbers rounded to nearest 10,000 from results shortly after the election)

Florida has 29 EC votes and a winning margin of 73,000 votes.
Ohio has 18 EC votes and a winning margin of 103,000 votes.
Virginia has 13 EC votes and a winning margin of 116,000 votes.
New Hampshire has 4 EC votes and a winning margin of 41,000 votes.

Total EC votes = 64. Total popular vote margin = 333,000.

Number of voters needed to switch = 333,000 / 2 = 166,500 voters.

If only 166,500 people in these four states had voted for Romney instead of Obama, the winning total of EC votes would have gone to Romney and he would have won.

What percentage of victory is 166,500 votes? It is 166,500 divided by the 121,745,725 votes cast. That is 0.136% of the total votes cast. Or, about 1/7 of 1%. That is a razor thin victory.

So how did Overland Park, KS, or Rancho Cucamonga, CA, or Fort Lauderdale, FL, or Tuscaloosa County, AL make all the difference in the election? As individual locales, they did not. However, each of these locations has a population just over the 166,500 needed to change the outcome of the election. 

One vote really does count when the margin of victory is so close.