(AP) - Seizing the campaign spotlight, vice presidential candidate Paul Ryan embraced "the calling of my generation" to help lead the country in tough times Wednesday night and pledged to cheering Republican National Convention delegates and a prime time TV audience that Mitt Romney will make the bold and difficult decisions needed to repair the nation's economy.

"After four years of getting the runaround, America needs a turnaround, and the man for the job is Governor Mitt Romney," the 42-year-old Wisconsin lawmaker declared in what amounted to a national debut. He spoke at a convention dogged by Tropical Storm Isaac, downgraded from a hurricane but still inflicting misery on millions along the nearby northern Gulf Coast.

"We will not duck the tough issues; we will lead," Ryan said.

His speech was part attack on Obama, part spirited testimonial to Romney, all leavened by a loving tribute to Ryan's own mother, seated across the hall in a VIP box. "To this day, my mom is a role model," he said while she beamed and exchanged smiles with one of his children and delegates cheered.

As for Obama and the Democrats, he said they 'have run out of ideas. Their moment came and went. Fear and division is all they've got left."

To the cheers of the delegates, he pledged Republicans would save Medicare from looming bankruptcy, despite constant accusations from Democrats that the GOP approach would shred the program that provides health care to more than 30 million seniors.

"Our nation needs this debate. We want this debate. We will win this debate," Ryan declared. But he offered no details of the remedy Republicans would propose.

Romney, in a secondary role if only for a moment, accused Obama of backing "reckless defense cuts" amounting to $1 trillion. Addressing the American Legion in Indianapolis, he said, 'There are plenty of places to cut in a federal budget that now totals over $3 trillion. But defense is not one of them."

In Tampa, the Romney team scripted an economy-and-veterans-themed program and kept a wary eye on Isaac. The storm remained a threat to levees in the New Orleans area almost exactly seven years after the calamitous Hurricane Katrina.

Inside the convention hall, delegates cheered a parade of party leaders past, present and - possibly - future.

The presidents Bush, George H.W., elected in 1988, and his son, George W., winner in 2000 and 2004, were featured in an evocative video. Arizona Sen. John McCain, the party's 2008 nominee, spoke on his 76th birthday and said he wished he'd been there under different circumstances. And an array of ambitious younger elected officials preceded Ryan to the podium, Sens. Rand Paul of Kentucky and John Thune of South Dakota among them.

Former Secretary of State Condoleezza Rice praised the Republican ticket in a speech that made no overt mention of Obama. "Mitt Romney and Paul Ryan will rebuild us at home and inspire us to lead abroad. They will provide an answer to the question, 'Where does America stand?'"

Ryan said in excerpts released in advance that he was accepting "the calling of my generation to give our children the America that was given to us."

He added, "The present administration has made its choices. And Mitt Romney and I have made ours: Before the math and the momentum overwhelm us all, we are going to solve this nation's economic problems.

"And I'm going to level with you: We don't have much time."

As he spoke a pair of electronic boards tallied the nation's growing national debt, approaching $16 trillion overall and more than $5 billion since the convention opened.

Ryan's vice presidential acceptance speech marked a prime-time national debut by a relatively young lawmaker lauded by fellow Republicans for his understanding of the complexities of the nation's budget.

Romney tapped Ryan this month as his running mate, a selection that cheered conservatives who have doubted the presidential candidate's own commitment to their cause.

If Ryan's selection was designed in part to appeal to conservatives, the convention was scripted to strengthen the ticket's appeals among women, Hispanics and others who prefer Obama over the Republicans, as well as veterans who supported McCain in 2008.

Romney delivers his own nationally televised acceptance speech Thursday night in the final act of his own convention. The political attention then shifts to the Democrats, who open their own convention on Tuesday to nominate Obama and Vice President Joe Biden for a second term.