Mitt Romney took a chance by picking Paul Ryan as his running mate, but the reaction to Mr Ryan's barnstorming speech at the Republican convention here on Wednesday suggests - for the time being at least - that the gamble is paying off.
For the first time this week, the atmosphere inside the Tampa Bay Times Forum caught fire, as the vice-presidential nominee delivered a withering attack on President's economic policies, delivered with the innocent charm of an eager-beaver boy scout troop leader.
Appearances were deceptive: the speech was riddled with facts stretched or downright wrong that Democrats instantly seized on – most notably the GM plant in his home district Mr Ryan claimed had had been closed under president Obama, in violation of a promise by visiting candidate Obama. In fact 98 per cent of the factory was shut down in 2008, when George W Bush was still in the White House.
Democrats also disputed claims that Obama policies had brought about last years US credit downgrade, when in fact the reason cited by the ratings agencies was Republican brinkmanship in Congress over authorising an increase the national debt ceiling.
But in a bitter campaign where truth has often been the first casualty, both sides have been guilty of manipulating the facts. The vigor of the Democratic response yesterday was implicit recognition of the danger posed by Mr Ryan, projecting sincerity and youthful change – much as Mr Obama did in 2008.
The speech, the most important of the 42-year-old Mr Ryan's career, has been widely deemed a smash. After being treated to two days of mostly listless oratory, delegates were galvanized. The danger, if anything, is that he set too high a bar for Mr Romney's own acceptance speech last night, highlighting the presidential candidate's inability to connect with an audience.
More pithily than anyone yet, the vice-presidential nominee summed up the argument that underpins the entire Republican campaign: "Without a change in leadership," he asked, "Why should the next four years be any different from the last four years?"
And as no other speaker this week, he caught the dispiriting mood of the times, marked by high unemployment and the fear that this young American generation would be worse off than its parents. "College graduates should not have to live out their twenties in their childhood bedrooms, staring up at fading Obama posters and wondering when they can move out and get going with life."
But the measure of Mr Ryan's success will be in the polls. Thus far he has given a small boost at best to Mr Romney, who is in a statistical dead-heat with Mr Obama. But there are signs he could tip his home state, Wisconsin, into the Republican column for the first time since 1984.
Face the facts: Speech dissected
Ryan blamed the Obama administration for the closure of the plant in his hometown, but GM announced the closure before President Obama was even elected.
Attacked President for "raiding" Medicare, but Ryan's budget recommends cutting the same amount of money from the programme as the Obama administration has.
Alleges the Obama administration ignored an urgent bipartisan report on debt, but the White House released a debt plan in response to the report in September.