In a heated exchange on Libya, he charged that "the broader problem is the unravelling of the Obama foreign policy, which is making the world more chaotic and less safe".
The debate in Danville, Kentucky took place as polls show Romney has enjoyed a bounce since their first televised debate last week began to change the dynamics of the race.
For the first time in more than a month Romney, a former Massachusetts Governor, has pulled ahead of Obama nationally and is closing the gap in the swing states.
A slew of polls this week show Republican voters are more enthusiastic about voting for Romney rather than against Obama. The challenger, a Mormon, has gained in particular among women voters. Also, according to Politico, 84 per cent of Republicans are more fired up and "extremely likely" to vote, compared with 76 per cent of Democrats.
Pollsters attribute Romney's steady climb to his aggressive debate performance against Obama, who has now admitted he had a "bad night" in the first of their three debates.
The President told a radio interviewer he had been "just too polite" in the 90-minute debate. Obama's next opportunity to shine will be at a town hall debate with Romney next Wednesday.
Biden's challenge in yesterday's debate was to do no harm to the President's re-election chances, a tough assignment for the gaffe-prone former Senator.
Apart from a disconcerting laugh during the first half of the debate, Biden used his experience to good effect. He won plaudits from a CNN instant poll of undecided voters when the candidates - who are both Catholics - were asked about their personal views on abortion.
The Vice-President also eclipsed Ryan, the House budget chairman, in a discussion of foreign policy, particularly on Syria, Iran and Afghanistan.
Despite the latest poll evidence about a swing towards Romney, it remains to be seen how much the debates will actually influence voters, with most people already saying they have made up their minds about the two candidates.
Even if Romney were to win the popular vote, he could still lose the presidential election. Because of the particularity of the US political system, in which the president is not directly elected, the victor is picked by an electoral college of 538 in which a majority of 270 electoral votes are required. As of yesterday, the University of Virginia's Centre for Politics predicted Obama could get the necessary votes.
Romney needs to win the key battleground states of Ohio, Florida, Colorado and Virginia to become the 45th president of the United States. Confirming the trend in his favour, the latest NBC News/Wall Street Journal/Marist polls show the Republican nominee one point ahead of Obama in Colorado and in a statistical tie in Virginia and Florida. But Obama still has a slight edge in Ohio.
