Brennan Linsley/AP Photo

BOULDER, Colo. - Voters in Colorado tonight got a glimpse of the Barack Obama of 2008, with his soaring, impassioned and relentless rhetoric that electrified a crowd in a way only rarely seen during the 2012 campaign.

Sharpening his closing argument for a second term, Obama delivered a forceful defense of his mantra of "change" in an evening rally at the University of Colorado, insisting that the economic and social transformation for which Americans are yearning will only come if voters stick by his side.

"You may not agree with every decision that I've made, you may be frustrated at the rate of change," he told the diverse crowd of 10,000 inside a campus basketball arena. But, "I know what real change looks like, because I fought for it," he added. "I've got the scars to prove it. I've got the gray hair to show for it."

With five days to go before Election Day, Obama is accusing his opponent, Republican nominee Mitt Romney, of acting like a "salesman," trying to masquerade as an agent of change, while in reality representing little difference in substance or policy from his Republican predecessor, former President George W. Bush. Deploying his campaign slogan, Obama claims he would move the country "forward," while Romney's proposals would take it "backward."

The president is taking his late-election case on a battleground state tour that will land him in Chicago on Tuesday. Earlier Thursday he stumped in Green Bay, Wis., and Las Vegas, Nev. On Friday he will spend the entire day at events in Ohio.

"I'm not going to allow this nation to be plunged into another battle over health care," Obama insisted tonight. "I'm not going to allow politicians in Washington to make health care choices for women that they can make for themselves…" The crowd roared.

"We need an agenda that recognizes that we don't just look out for ourselves, we look out for one another," he said.

Invoking the ideals that his aides say shaped his first run for political office in Illinois, Obama said he is running to be a "champion" for the people who "need a champion in Washington."

"I ran because the voices of the American people, your voices, had been shut out of American politics for way too long," Obama said.

He acknowledged there have been some "big fights" over the past four years to achieve his goal, but said "I'm not ready to give up on that fight."

"We've come too far to grow faint-hearted! Now's the time to keep pushing forward!" Obama exhorted the crowd which was on its feet with cheers and applause.