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President Obama today argued that the growing gap between the nation's rich and poor poses "a fundamental threat to the American dream," as he outlined a sweeping economic agenda expected to dominate the remainder of his presidency.

Repeating familiar themes, Obama said "a dangerous and growing inequality and lack of upward mobility" is jeopardizing the basic American middle-class tenet that "if you work hard, you have a chance to get ahead."

"This is the defining challenge of our time: making sure our economy works for every working American. That's why I ran for president. It was the center of last year's campaign. It drives everything I do in this office," he said, in remarks he made at an arts and education town hall recreation center in the Anacostia neighborhood of Washington. An official said his remarks preview his State of the Union address.

The president's 50-minute landmark speech was intended to reframe the public debate as he seeks to move past the troubled Obamacare rollout that has consumed Washington for the past two months.

Acknowledging the "poor execution" by his administration, he admitted, "We didn't roll out parts of this law as well as we should have." But he also blamed Republicans and their "reckless shutdown" of the government for why Americans are fed up with Washington.

"Nobody has acquitted themselves very well these past few months. So it's not surprising that the American people's frustrations with Washington are at an all-time high," he said.

To boost job creation and lessen economic disparity, the president reiterated his call for a higher minimum wage, more early childhood education and investments in infrastructure. He did not, however, outline any new legislative initiatives.

The president also continued to tout the economic benefits of the Affordable Care Act, claiming his signature law will help level the inequalities that existed in the broken health care system.

"This law's going to work," he said. "And for the sake of our economic security, it needs to work."

Obama once again challenged his Republican opponents to put forth their own plans to expand economic opportunity, increase wages and reform health care.

"You owe it to the American people to tell us what you are for, not just what you're against," he said to applause. "That way, we can have a vigorous and meaningful debate. That's what the American people deserve. That's what the times demand."