Obama had stops planned in all three states over the next week.
Smiling anew, the president spoke to the largest crowd of the campaign on Thursday afternoon, about 30,000 people in the college town of Madison, Wis.
As the president mockingly searched for the "real Mitt Romney" during an earlier speech in Denver, Vice President Joe Biden pounded the message in Iowa, another toss-up state.
"Ultimately, presidential races, unlike any other race, get down to character," Biden said. "They get down to the character of the man or woman and the character of their convictions: Do they mean what they say and will they do what they say."
AP White House Correspondent Ben Feller in Washington contributed to this report.
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