TAMPA, Fla. -- Rep. Paul Ryan on Wednesday electrified the crowd at the GOP convention with a speech that taunted President Obama for a failure of leadership, promising that he and Mitt Romney will win the contest of ideas during the campaign.

"They have no answer to this simple reality: We need to stop spending money we don't have," he said.

"The man assumed office nearly four years ago. Isn't it time he assumed responsibility?"

Speaking about the issue of Medicare, but making a larger rhetorical point, Ryan told the fired-up delegates, "Our nation needs this debate, we want this debate, we will win this debate."

And he vowed, "The greatest threat to Medicare is Obamacare, and we're going to stop it. Medicare is a promise and we're going to honor it."

The seven-term congressman from Wisconsin derided the president's belief in government as a solution to so many of the nation's ills, from righting the economic recession to controlling the soaring costs of health care.

"By his own decisions, President Obama has added more debt than any other president before him, and more than all the troubled governments of Europe combined. One president, one term, $5 trillion in new debt," Ryan said.

He talked about the downsized aspirations of America's young people under Obama's failed economic policies.

"College graduates should not have to live out their 20s in their childhood bedrooms staring up at fading Obama posters and wondering when they can move out and get going with life," he told an audience that interrupted his speech with applause 60 times.

The president's record after one term in office failed to live up to the promise of Obama's 2008 campaign, which enticed Americans with promises of hope and change, Ryan said.

"It all started off with stirring speeches, Greek columns, the thrill of something new," Ryan said. "Now all that's left is a presidency adrift, surviving on slogans that already seem tired, grasping at a moment that has already passed, like a ship trying to sail on yesterday's wind."

Ryan, 42, vowed to help Romney repeal Obama's health care reforms and to slash federal spending. He also promised to strengthen Medicare even though his own budget blueprint would fundamentally transform the entitlement program from one that pays for medical care to a voucher-style program that would help beneficiaries buy private insurance.

"It began with a financial crisis. It ends with a job crisis," he said. "It began with a triple-A credit rating for the United States. It ends with a downgraded America."

"After four years of getting the runaround, America needs a turnaround," Ryan said, "and the man for the job is Gov. Romney."

Many of the delegates were conservatives who were wary of Romney but enthusiastically supportive of his vice presidential pick, a man who as chairman of the House Budget Committee offered to put down on paper their vision of a drastically smaller government that spends less, taxes less and is far less intrusive into individual lives.

Ryan introduced his family to the crowd and America, spoke directly about the generational difference between him and Romney, and waxed eloquently about a life spent in the tiny Wisconsin hamlet of Janesville.

"He is dynamic and he's charismatic," Michael Heyer, a Wisconsin delegate who owns two wholesale bakeries in Milwaukee, told The Washington Examiner. "I think he is the real strength behind Mitt."