Chicago (CNN) - With an increasingly insurmountable delegate lead over his Republican opponents and the wind at his back heading into Tuesday's Illinois primary, Mitt Romney sought Monday to re-frame the presidential contest as a battle between himself and President Barack Obama over the future of the economy.
Speaking at the University of Chicago's Harris School of Public Policy, where Obama once served on the advisory board, Romney said the president has pursued an "assault on freedom" with stifling business regulations and high taxes.
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Romney made no mention of his GOP foes.
"This November, we face a defining decision," Romney told an audience largely comprised of college students, reading off teleprompter. "Our choice will not be one of party or personality. This election will be about principle. Our economic freedom will be on the ballot. And I intend to offer the American people a clear choice."
Over and over again, Romney returned to the theme of "freedom," attacking Obama's understanding of the concept.
But substantively, there was little new in Romney's remarks aside from a couple of references to struggling workers he has met along the campaign trail.
Instead, one Romney adviser said the main goal of the speech, both in message and in setting, was to demonstrate "contrast" with the president.
"For three years, President Obama has expanded government instead of empowering the American people," he said. "He's put us deeper in debt. He's slowed the recovery and harmed our economy. And he has attacked the cornerstone of American prosperity, our economic freedom."
Romney said President Obama's "heavy hand" has cast a pall of uncertainty over the economy, preventing entrepreneurs from investing or starting small businesses.
Inventors like Thomas Edison, the Wright brothers and Steve Jobs would have never have succeeded in the current economy, Romney claimed.
The Obama campaign arranged a conference call Monday afternoon to respond to Romney's speech, and his chief GOP rival Rick Santorum mocked Romney for promoting "freedom" while also having passed a health insurance mandate in Massachusetts.
"Let's just be brutally honest about it," Santorum said at an event in Dixon, Illinois. "There is one candidate in this race who can never make this race about freedom because he simply abandoned freedom when he was governor of Massachusetts and he abandoned it when he promoted Obamacare in 2009."
Romney took three pre-screened questions from the audience after his speech, including one about how students would be better off under President Romney.
He pointed to the growing deficits in Washington and said young people should vote Republican because they are trying to avoid passing on debts to future generations.
"I don't mean to be flip with this," he said. "But I don't see how a young American can vote for a Democrat. I apologize for being so offensive in saying that while I catch your attention, but I mean that in the humor, I mean, there's some truth there."
UPDATE: In their call responding to the speech, Obama advisers said independent tax analysts have concluded that Romney’s tax plan will increase deficits by five trillion dollars over the next ten years.
They also took aim at Romney’s repeated claim that the regulatory climate is slowing economic production.
Princeton economics professor Cecilia Rouse, a former member of the president’s Council of Economic Advisers, said there is “not actually any evidence that regulatory burden actually has a meaningful impact on employment or the economy now.”