They represent 44 percent of the electorate and back President Obama 2 to 1 over Mitt Romney, but they are unlikely to make a difference on Election Day.

A USA Today/Suffolk University poll published Wednesday shows Obama leads his Republican challenger by a wide margin among registered voters who say they probably won’t cast ballots this fall. In the survey, 43 percent of unlikely voters said—if they were to vote—they would vote for Obama; 20 percent said they would vote for Romney, and 18 percent said they would vote for a third-party candidate.

Forty-four percent of unlikely voters said they voted for Obama in 2008 but probably won’t vote at all this year. Reasons not to vote ranged from not liking either candidate to believing a vote does not matter.

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The Obama campaign has stressed the importance of voter turnout to the president’s reelection prospects.

“This is going to be a close election,” Obama adviser David Plouffe said on NBC’s “Meet the Press” in June. “Listen, we’re running a grass-roots campaign. We believe in registering voters, turning them out, neighbors talking to neighbors. Our campaign is building, I think, the best grass-roots operation you’ve ever seen to win a close race. But, again, this is going to come down to a few states.”