(CNN) – Polls assessing the state of the presi

(CNN) – Polls assessing the state of the presidential race typically survey people likely to vote in November's general election. But what about the millions of Americans who could cast ballots, but won't?

A  USA Today/Suffolk University poll released Wednesday found that of the roughly 40% of eligible Americans who aren't likely to vote in November, 2-in-1 would support President Barack Obama. Voters who are registered, but not likely to vote, back Obama over his Republican challenger Mitt Romney, 43%-20%. Another 18% said they'd support a third party candidate, and 15% weren't sure who they would vote for.

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Among eligible voters who weren't registered, the numbers were similar. Forty-three percent backed Obama, while 14% supported Romney and 23% said they'd go for a third party.

In 2008, 64% of voting-age citizens – 131 million in total – cast ballots in the presidential election, according to the U.S. Census Bureau. That was not statistically different than the number who voted in 2004, though it was higher than the number who voted in presidential elections in 2000 and 1996.

The USA Today/Suffolk poll of unlikely 2012 voters indicated that only 32% did not vote in 2008. Forty-four percent cast ballots for Obama, and 20% said they voted for McCain.

Why aren't people voting? Fifty-nine percent find that 'nothing ever gets done; it's a bunch of empty promises.' Fifty-four percent find politics corrupt, and 42% do not know the difference between Democrats and Republicans. Thirty-seven percent believe that politics do not make a difference in their lives.

In Wednesday's poll, 55% of the non-likely voters said they had a favorable opinion of Obama, compared to 25% who had a favorable opinion of Romney. Many more, however, remained undecided on Romney. Twenty-two percent were undecided on the presumptive Republican presidential nominee, compared to only 7% who were undecided on Obama.

Of the Americans polled who were eligible to vote but were not registered, 26% said they were too busy to get themselves on the voter rolls. Twelve percent said their vote wouldn't count anyway, and 10% said they just didn't want to get registered.

Americans registered to vote but unlikely to actually cast ballots had similar rationale for not participating in this year's election. Twelve percent said their vote wouldn't count, and 13% said it was their right to choose not to vote. Fourteen percent, however, said they may wind up voting, or that they were thinking about voting, in November.

However, just because eligible voters are choosing not to cast a ballot does not mean that they do not second guess their decision. Fifty percent of the unlikely voters believe it will bother them that they are allowing others to elect their president. Forty-one percent said it wouldn't bother them, since they felt their vote doesn't make a difference.

The USA Today/Suffolk University poll surveyed 800 adults by telephone between July 30-August 8. The sampling error was plus or minus 3.47 percentage points