ANALYSIS: Election 2012 Numbers Don't Always Add Up

Oct. 19, 2012 -- We're going to see a slew of numbers between now and Election Day, and they're not always going to add up.

Take, for example, yesterday's Gallup tracking poll that showed Romney up by 7 percentage points among likely voters nationally, 52 percent for Romney compared to 45 percent for Obama.

Compare that to a duo of NBC News-Wall Street Journal-Marist polls that found President Obama at 51 percent in two key swing states -- up 8 points over Romney in Iowa (51 percent to 43 percent) and up 6 points over the Republican challenger in Wisconsin (51 percent to 45 percent).

The latest polling suggests a couple of things, according to ABC News Political Director Amy Walter:First, one of these is terribly off -- it is impossible to live in a world where Romney is leading nationally by seven points and yet trailing in a battleground state like Iowa by eight points.

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Second, the margins of the polls are off, but the premise is correct: Romney is doing better in national polls, but continues to trail in Electoral College math. And that scenario, while rare, is looking highly possible. How would that happen?

Here's how: Romney over-performs in the South and even some blue states which would goose his national popular vote numbers. But, millions of dollars of attack ads have kept his vote ceiling low in many of these swing states. He can close the gap, but never overcome Obama in key swing states like Ohio, Iowa and Wisconsin.

Take a look at the Electoral College map: Both sides agree that North Carolina, Florida, Virginia and Colorado are the best pick-up opportunities for Romney. If he gets all of those he's at 257. But, Iowa, Wisconsin, New Hampshire and Nevada are most likely to stay in Obama column. That gives the president 263.

That leaves Ohio, with its 18 Electoral Votes, as the decider.

Democrats concede the race has tightened there but they are as confident that they are going to win it as ever. Republicans argue that it is very, very close in the Buckeye State -- much closer than the public polls have it -- but they aren't putting it into their column just yet.