No one was more surprised about the size of President Obama’s four-point victory over Mitt Romney last November than the Romney campaign. But no one’s reputation suffered a worse possible setback from the outcome than Gallup, whose final pre-election poll showed Romney leading by one.

After their big miss, Gallup editor-in-chief Frank Newport promised a comprehensive investigation into what happened in 2012. On Monday, the firm released its findings, identifying four main reasons why it understated Obama’s support: 1) faulty likely-voter screen; 2) undersampling the east and west coasts; 3) oversampling whites; and 4) undersampling cell phones.

On the faulty voter screen, the Hotline‘s Steve Sheppard reports:

The report found the question seemingly most responsible for tilting their poll too far toward Romney was asking respondents how much thought they were giving to the election. Obama led by 3 percentage points among all voters, but that swung 4 points toward Romney among voters identified by Gallup as likely to cast ballots.

[University of Michigan professor Michael] Traugott said it’s possible the Obama campaign’s focus on battleground states requires a different approach to identifying likely voters in those states. “Polling firms don’t organize the geography of the samples by focusing on battleground states versus non-battleground states, he said,” but turnout “actually was up” in these states, despite national declines.

“One of the interesting things about this is whether or not this is a factor that is idiosyncratic to the 2012 campaign” and a testament to the Obama campaign’s skill and efficiency in turning out their voters in battleground states, Traugott said.

And that really is the big question facing not just Gallup but the Republican Party as well. Now that Obama will never be on a ballot again, what does the American electorate really look like? Does it look like the America that voted in 2008 and 2010? Or does it look like the America that voted in 2012?

Like Gallup, we’ll begin to find out when Virginia and New Jersey go to the polls next November.