Obama touched on a host of issues that form the core of his second-term economic agenda, including improving his signature health-care law, making college more affordable and making sure women receive equal pay for equal work.

He criticized Republicans for their budget plans, for blocking the minimum wage increase and their repeated attempts to repeal the health-care law.

"The Republicans' refusal so far to raise the minimum wage is pretty consistent with their general world view, which says, basically, 'You're on your own, government doesn't have a role to play in making sure that the marketplace is working for everybody,'" he said.

Party Appeal

While there's little chance a minimum wage bill will pass this year over the solid opposition of Republicans, who have the majority in the U.S. House, Democrats are using it to whip up the party's base for the coming campaign.

Democrats are at risk of losing control of the U.S. Senate in November, party because of voter dissatisfaction with the president as well as a lack of enthusiasm within the coalition of minority and young voters and women who helped propel Obama to two terms as president.

Democrats also are fighting history. The party in control of the White House has lost ground in the Senate in 12 of 17 midterm elections since the end of World War II.

The need to energize the party base has been a frequent theme for Obama and his advisers.

"During presidential elections, young people vote, women are more likely to vote, blacks, Hispanics more likely to vote," Obama told donors at a March 20 fundraiser for the Democratic Congressional Campaign Committee in Miami. "But in midterms we get clobbered, either because we don't think it's important or we've become so discouraged about what's happening in Washington that we think it's not worth our while."

Florida Vote

He made those remarks just a week after Democratic candidate Alex Sink lost to Republican David Jolly in a special election in Florida's 13th Congressional District, 48.4 percent to 46.6 percent. Obama won the Tampa Bay-area district in 2012. Although it had been in Republican hands for four decades, an influx of young people, Hispanics and blacks had fueled Democratic hopes of taking the district back.

David Plouffe, a onetime White House senior adviser and strategist for both of Obama's presidential campaigns, called the result "a screaming siren" warning the party that it needs to do more to motivate supporters in November.

Young Voters

Representative Gary Peters, a Michigan Democrat who is seeking a fourth term in November, accompanied Obama to the University of Michigan.

"Certainly it's important for college students to be engaged, and the momentum from 2012 we hope carries forward to 2014," he said in an interview before Obama's speech.

In a George Washington University-Battleground Poll released March 25, Democratic pollster Celinda Lake and Republican partner Ed Goeas found that Republican voters are more energized to vote than Democrats.

Sixty-four percent of Republicans said they are "extremely likely" to vote in November, compared with 57 percent of Democrats, they said in an analysis of the results.

Some of that motivation may come from opposition to the Patient Protection and Affordable Care Act, the law known as Obamacare. Republicans sought to make the Florida special election a referendum on the law and party leaders that will be their strategy for November.

While 64 percent of Americans support keeping the Affordable Care Act intact or with small changes, a Bloomberg poll last month also showed that the opponents were the most motivated bloc, with 73 percent of the people favoring repeal saying they'd go out and vote.

Voter Support

Fresh off announcing yesterday that enrollment for insurance under his signature health-care law had hit 7.1 million, Obama returned today to an issue where polls show the public solidly on his side. Raising the minimum wage was supported by 69 percent of Americans, including 45 percent of Republicans, in the Bloomberg poll.

Obama's also been trying to keep Hispanic voters from defecting or not voting. Obama's approval rating among Hispanics has dropped 22 points since last May to 51 percent, according to Gallup polling last month. He won 71 percent of the Hispanic vote in 2012.

The president last month ordered the Homeland Security department to find ways to be more humane when it enforces immigration laws, a key issue with Hispanics.

–With assistance from Roger Runningen in Washington and Toluse Olorunnipa in Tallahassee, Florida.