Republican VP choice Paul Ryan promises US 'turnaround'
Republican vice-presidential candidate Paul Ryan has promised a "turnaround" for America, in a prime-time speech to the party convention in Tampa, Florida.
The Wisconsin congressman said he and Republican White House nominee Mitt Romney would not duck the tough issues.
Arizona Senator John McCain, the 2008 Republican presidential nominee, and former Secretary of State Condoleezza Rice also took to the podium.
Mr Romney will challenge Barack Obama for the White House in November.
"After four years of getting the run-around, America needs a turnaround, and the man for the job is Governor Mitt Romney," Mr Ryan said in Wednesday's speech.
But the Obama campaign and independent fact checkers questioned a number of Mr Ryan's points, among them his claim that the president sliced $716bn (£450bn) from the Medicare programme for Americans over 65.
'Fading Obama posters'
On the second full day of the convention, Mr Ryan also said: "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 that much time."
In his biggest appearance yet on the national stage, the 42-year-old chairman of the House of Representatives budget committee accepted the vice-presidential nomination.
"We will not duck the tough issues - we will lead," Mr Ryan said. "We will not spend four years blaming others - we will take responsibility.
"The work ahead will be hard. These times demand the best of us - all of us - but we can do this."
In one of the biggest applause lines of the night, Mr Ryan said: "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 pledged that a Romney-Ryan administration would create 12 million American jobs in its first term and cap federal spending at 20% of gross domestic product.
Obama attack ad
Speaking earlier, Senator McCain lambasted the Obama foreign policy, saying the president was not true to American values, and that he had abandoned Syria's people to a "savage and unfair fight".
"The demand for our leadership in the world has never been greater," the senator said. "People don't want less of America. They want more."
Condoleezza Rice praised the Republican ticket in a speech that made no overt mention of President Obama.
"Mitt Romney and Paul Ryan will rebuild us at home and inspire us to lead abroad," she said. "They will provide an answer to the question, 'where does America stand?"'
Ahead of Mr Ryan's address, the Obama campaign released an attack video branding the Republican a politician from "a bygone era".
The film draws attention to his budget plans that would see tax cuts for the wealthy, while overhauling popular social programmes such as Medicare, in order to reduce government spending.
The video says that Mr Ryan's vision for the country is "anti-female", adding that he opposes abortion and has co-sponsored legislation that used the term "forcible rape".
Mr Romney, 65, spent Wednesday away from Tampa, speaking to veterans in Indianapolis, Indiana, a day after the Republican convention officially nominated him for president.
He is scheduled to deliver his big speech to the convention on Thursday night, and formally accept his party's nomination.
On Tuesday night, Mr Romney's wife, Ann, made a speech to the party convention directly appealing to women voters, a key voting bloc with whom Mr Romney has trailed Mr Obama in opinion polls.
At one point she called out: "I love you women!"
Ann's Latino lunch
Mr Romney, a former governor of Massachusetts and private equity chief, has had trouble connecting with voters at a personal level. The Romney campaign is said to view his wife as a "secret weapon" who can help boost his appeal.
On Wednesday, Mrs Romney attended a luncheon called Women for Romney with Janna Ryan, the wife of running mate Paul Ryan.
Later, Mrs Romney appeared at a Latino Coalition lunch, where she addressed criticism that Republicans "don't care about this community. That's not true. We very much care about this community."
She also said Latinos "are mistaken if they think they are going to be better off" under a second Obama term.
President Obama's re-nomination will be confirmed next week at the Democratic National Convention in Charlotte, North Carolina.