Republican presidential candidate Mitt Romney got a strong testimonial from his vice presidential running mate, Wisconsin Congressman Paul Ryan, who generated the most enthusiasm so far at the Tampa convention with his address.

Mr Ryan energised Mr Romney’s White House bid on Wednesday with a scathing take-down of Barack Obama’s economic record.

Adding youthful vim and policy vigour to the Romney ticket, the 42-year-old rising star received a standing ovation for his impassioned pitch to American voters 10 weeks from election day.

“I accept the duty to help lead our nation out of a jobs crisis and back to prosperity. And I know we can do this,” Mr Ryan said while accepting his nomination, exhibiting little sign of nerves during his 35-minute speech.

Mr Ryan accused Mr Obama of saddling the US economy with four years of failed big government policies and held upMr Romney, a 65-year-old former Massachusetts Governor, as the man to turn things around with his business acumen.

“After four years of getting the run-around, America needs a turnaround, and the man for the job is Governor Mitt Romney,” he said.

Mr Romney was formally taking up the nomination with his all-important acceptance speech to the convention in Tampa, Florida yesterday, the climax of three days of rousing addresses by party grandees and rising stars.

He lies neck-and-neck with Mr Obama in national polls ahead of a November 6 election that should be the challenger’s for the taking, given the sour economy and stubbornly high unemployment.

Mr Romney’s vice presidential pick was seen as crucial four years after John McCain electrified conservatives by choosing inexperienced Alaska Governor Sarah Palin, only to see her wither in the national spotlight.

Democrats have portrayed Mr Ryan as an extreme, budget-cutting friend of the rich who would gut beloved social programmes.

But Republicans have used the selection of the seven-term congressman, whose budget plan is the party’s blueprint to fix the flagging US economy, to breathe fresh life into a race that had been in danger of drifting away from Mr Romney.

Mr Ryan took his chance in the convention spotlight to assail the President’s record, saying Mr Obama’s promises of hope and change had fallen flat after four years of fiscal recklessness, ballooning debt and joblessness.

“It all started off with stirring speeches, Greek columns, the thrill of something new,” he 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.”

His address, carried live on cable TV across America at prime time, contained a clear pitch to working class and middle class Americans who may find it hard to identify with Romney’s background of wealth and privilege.

The Obama campaign had upped the pressure on Mr Ryan in the hours leading up to the speech, releasing a new web video accusing him of favouring outdated top-down economics, tax cuts for the wealthy and the replacement of the popular Medicare programme for the elderly with a voucher system.

Speeches earlier on Wednesday by Senator John McCain and former Secretary of State Condoleezza Rice focused on foreign policy – which has taken a back seat to the economy in the campaign – saying Mr Romney would restore US leadership in the world.

They accused Mr Obama of letting down Israel and other allies.

Mr Romney was meanwhile preparing for his own address yesterday, when he was to formally accept the nomination and make his own case to a prime-time audience in perhaps the most important speech of his political career.

Republican vice presidential candidate Paul Ryan with his family and mother waving to the crowd at the 2012 Republican National Convention in Tampa, Florida.

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