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ABC News' Mary Bruce and Devin Dwyer Report:

Invoking Theodore Roosevelt's progressive agenda, President Obama today portrayed himself as a champion of the middle class as he underscored the populist themes of his 2012 campaign.

"This isn't just another political debate. This is the defining issue of our time. This is a make or break moment for the middle class, and all those who are fighting to get into the middle class," the president said in Osawatomie, Kan., as he delivered a wide-ranging indictment of the nation's economic disparity.

At stake, the president cautioned, is the fundamental American principle "that this is the place where you can make it if you try."

Obama spoke in the same small town where Theodore Roosevelt outlined his vision for a "New Nationalism" over a century ago. Although "Roosevelt was called a radical, a socialist, even a communist," Obama said we are a "richer nation and a stronger democracy" because of his vision of economic fairness and equal opportunity.

Read more about Obama invoking Theodore Roosevelt.

Meet the oldest woman in Osawatomie, who saw both presidents 100 years apart.

The president accused Republicans of suffering from "collective amnesia" about the financial crisis. "Their philosophy is simple: we are better off when everyone is left to fend for themselves and play by their own rules," he said. "Well, I'm here to say they are wrong."

"I'm here to reaffirm my deep conviction that we are greater together than we are on our own. I believe that this country succeeds when everyone gets a fair shot, when everyone does their fair share, and when everyone plays by the same rules. Those aren't Democratic or Republican values; 1% values or 99% values. They're American values, and we have to reclaim them," Obama told the crowd of 1,200 at Osawatomie High School.

The president went on to assail trickle-down economics, saying "it fits well on a bumper sticker," but "here's the problem: It doesn't work. It's never worked."

"We simply cannot return to this brand of your-on-your-own economics if we're serious about rebuilding the middle class in this country. We know that it doesn't result in a strong economy. It results in an economy that invests too little in its people and its future. It doesn't result in a prosperity that trickles down. It results in a prosperity that's enjoyed by fewer and fewer of our citizens," he said.

While Obama's 55 minute-long speech lacked new ideas for righting the U.S. economy, the president used the opportunity to turn up the heat on Republicans for failing to pass a payroll tax cut extension. Obama warned that if Congress fails to extend the tax cut, set to expire at the end of this month, 160 million American will see their taxes go up by an average of $1,000.

"We have to ask ourselves: Do we want to make the investments we need in things like education, and research, and high-tech manufacturing? Or do we want to keep in place the tax breaks for the wealthiest Americans in our country? Because we can't afford to do both. That's not politics. That's just math," he said.

Meanwhile, Republicans accused the president of failing to provide concrete ideas to rebuild the economy. "Maybe instead of trying to be like other presidents, Obama should try being president. The president continues to rehash the same ideas and policies when what Americans want is progress. The fact remains the president is desperately trying new slogans and messages to see what sticks because he can't figure out how to sell his last three years of high unemployment and more debt. Reality is he's failed to lead or live up to the promises he's made," Republican National Committee spokeswoman Kirsten Kukowski said.