Paul Ryan, a hero to conservatives and lightning rod for Democrats, has accepted the Republican nomination as Mitt Romney's vice presidential running mate, saying the moment for President Barack Obama's Democrats "came and went".
Mr Ryan's nationally-televised speech on the second day of the storm-shortened Republican National Convention in Tampa, Florida, was a debut of sorts for the 42-year-old congressman from the Midwestern state of Wisconsin.
Though a leader on budget policy in Congress, Mr Ryan was not well-known outside Washington when tapped by Mr Romney this month.
The selection of Mr Ryan, author of a plan to reduce the government deficit, excited Republicans sceptical of Mr Romney's commitment to conservative principles. But Democrats pounced, saying Mr Romney, the former governor of Massachusetts, was now clearly wedded to Mr Ryan's proposals to cut spending by revamping health care programmes for the elderly and poor.
To the adoring cheers of the Republican faithful, Mr Ryan said Democrats "have run out of ideas. Their moment came and went. Fear and division is all they've got left".
He said Mr Romney would not duck the difficult decisions needed to repair the economy. "After four years of getting the runaround, America needs a turnaround, and the man for the job is Governor Mitt Romney," he said.
Mr Romney and Mr Ryan were formally nominated in roll call votes on Tuesday. Mr Romney accepts his party's nomination in a nationally-televised speech later, the third and final full day of the convention.
But he may find Mr Ryan a tough act to follow. His speech was part attack on Mr Obama, part spirited testimonial to Mr Romney, all leavened by a loving tribute to Mr 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.
Mr Ryan's youthful energy and down-to-earth appeal stands in contrast to the stiffer, more aristocratic Mr Romney, 65. He drew laughs in his speech joking about Mr Romney's musical tastes.
However, so far Mr Ryan has not changed the dynamics of the presidential race. Polls continue to show Mr Romney and Mr Obama in a statistical tie ahead of the November vote.