After stumbling badly during the first debate, the president made the bailout an early topic during the second. He raised it again during the candidates' final encounter, which was supposed to be about foreign policy.
"If we had taken your advice ... about our auto industry, we'd be buying cars from China instead of selling cars to China," Obama said.
A defensive Romney retorted: "I'm a son of Detroit. ... I would do nothing to hurt the U.S. auto industry."
But by then, the argument was a moot point for most Ohio voters. Nearly seven in 10 had made up their minds before September, the exit polls showed.
With time running out, Romney strategists gambled by airing television and radio ads in Ohio that claimed Obama's policies had led GM and Chrysler to build cars in China. The move backfired, drawing sharp rebukes from both companies.
"It was very misleading, to be kind. It really upset a lot of our people," said Dave Green, president of a United Auto Workers local representing about 1,500 workers at a plant in Lordstown.
Obama won Michigan by a comfortable margin but took Ohio with just over 50 percent of the vote. Despite his steadfast support of organized labor, many blue-collar autoworkers were torn because of disagreements with the president over issues such as guns and abortion, Losier said.
That's where the bailout may have tipped the scales. Union members who backed the president lobbied wavering co-workers, reminding them how dire their situation had been when Obama took office.
"There was a real belief that they were going to liquidate our facility," Green said. "People were walking around with clipboards taking inventory. It did not look good. The polls were all saying, 'Don't rescue the auto companies.' But he did it anyway."
In the end, Green said, the choice came down to a simple question: "Who are we going to vote for — the guy who was trying to push us down the river or the guy who was throwing us a life vest?"
The bailout was popular with independents and even some Republicans, and drew support for Obama outside the usual Democratic-leaning areas, said Chris Redfern, chairman of the Ohio Democratic Party.
Frank Hocker, a retiree who once worked at a truck manufacturing plant in Springfield, said he wasn't a single-issue voter. But when Obama "stuck his neck out and did the right thing with General Motors, you know, that satisfied me."
Associated Press writers Justin Pope and Tom Krisher in Detroit and Julie Carr Smith and Ann Sanner in Columbus contributed to this report.