Midway through his boisterous rally, Senator McCain stopped to say: "What a crowd. What enthusiasm.
Three weeks ago, the AP-GfK survey put him eight points in the lead.
With the drawcard of two popular Republican women - his running-mate, Sarah Palin, and country music star Gretchen Wilson, who sang Redneck Woman -- more than 12,000 people filled an airport hangar in Ohio's most conservative city.
She said flying into Cincinnati, she had been amazed to look down and "see my face ploughed into a cornfield".
As the crowd chanted "Sarah, Sarah" and "Mac is Back", they also booed whenever Senator Obama's name was mentioned.
Julie and George Thomas came along to the rally with five-year-old daughter Emily, who has cerebral palsy.
They said it was a bonus to see Mrs Palin, whose son, Trig, has Down syndrome and is also a special needs child.
Mr Thomas said he had considered bringing along a home-made sign reading "No More Mr Nice Guy" to urge Senator McCain to start taking the fight up to Senator Obama.
"I like the fact he's a true American hero," he said of Senator McCain, adding he had very "serious, serious concerns" about Senator Obama.
"Trust. Lack of being forthcoming on his past, lack of releasing information about the past," he said, citing Senator Obama's past associations with 1960s radical Bill Ayers and his former firebrand pastor, the Rev Jeremiah Wright.
George Hillis, 72, said he would never vote for Senator Obama because he was a "liar" and "has an extensive radical background associating with people who are not the type of people we want running the country".
Mr Hillis said he believed Senator McCain would win the election, despite what the polls said, because the silent majority of voters had started grumbling.
"We're starting to talk. We don't waste our breath until the election comes, but there's a movement going on now," he said.
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