The Illinois senator also took a swipe at embattled Attorney General Alberto Gonzales. Obama has joined several other Democrats in calling for Gonzales to resign.

"I was a constitutional law professor, which means unlike the current president I actually respect the Constitution," Obama told an audience at a campaign fundraiser. "I believe in an attorney general who is actually the people's lawyer, not the president's lawyer."

Obama's remarks drew one of the most enthusiastic responses in a speech often interrupted by applause.

Gonzales acknowledged Friday there is confusion about his role in firing the eight U.S. attorneys last fall. His former chief of staff, Kyle Sampson, told Congress Thursday that prosecutors put on a list to be fired got there in part because they were not deemed "loyal Bushies."

Responding to Obama's comments, Dan Ronayne, a spokesman for the Republican National Committee, said, "Senator Obama needs to understand that at this level words matter and he will be scrutinized."

Ronayne pointed that Obama was only a senior lecturer and not a full professor. The University of Chicago lists him as a senior lecturer on leave.

During his stop in Florida, Obama held a brief meeting with Democratic lawmakers and then spoke for about three minutes to more than 100 college students who held an impromptu rally outside an IMAX theater where he held his fundraiser.

"I just hope that everyone here has that same sense of urgency that I do," Obama told the students. "I hope the young people in particular use this campaign as a vehicle to get involved and engaged. This is one of those rare moments where we could change history, and those moments don't come that often. So I hope that all of you take advantage of it."

Inside the fundraiser, which was a sellout at 640 tickets and raised about $150,000, people packed a room and balcony.

Obama told the group that he can unite the country, and a united country will bring change.

"But there are going to be times when I'm tired, there are going to be times when I'm weary, there are going to be times when I make mistakes, but none of that matters if we have millions of voices who are coming together insisting on a new America," he said.

At the Capitol, Obama signed books for a handful of lawmakers before inching his way through a packed room.

"One of the things that I've come to realize is how much I learn in the state Legislature, because there's very few jobs that give you a better sense of the state and the people in it — the struggles they're going through every day," Obama said. "It was that experience in the Legislature that convinced me that politics can be a noble calling."

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Associated Press writer Stephen Majors contributed to this report.