Ryan, accustomed to defending a controversial budget plan, didn't back down, and he didn't seem to lose his cool. He projected a confidence that Biden's 2008 rival, then-Alaska governor Sarah Palin, failed to do in their debate four years ago. "I know you're under a lot of duress to make up for lost ground," Ryan told Biden at one point, "but I think it would be better if we stop interrupting each other."
Biden was energetic, engaged and combative in a way President Obama failed to be in his performance against Republican Mitt Romney in Denver last week. The question was whether he came across as convincing or rude. His aggressive demeanor may have been designed more to reassure Democratic partisans than to appeal to swing voters who tend to be less enamored of political warfare.
Either way, his performance couldn't be characterized as an empty chair, as Obama was on a New Yorker cover after the Denver debate. The running mates' encounter was faster paced and more immersed in policy details than the debate last week.
How much difference will it make?
Vice presidential debates typically don't matter much. Even the running mates' debate that had the clearest "winner" Lloyd Bentsen after his memorable putdown of Dan Quayle as "no Jack Kennedy" didn't rescue the 1988 election for the Democratic ticket. It was Quayle, not Bentsen, who was sworn in as vice president in January 1989.
This time, though, it's possible the running mates' debate could be of more consequence than usual in a campaign that is suddenly closer than ever and still in some flux.
Biden's supercharged performance was aimed at stemming the Republican ticket's momentum since the last debate. Ryan, known as a fan of the PowerPoint, seemed to be doing his best to respond not in the language of the House budget chairman but in the words of a native of Janesville, Wis.
When the question involved the war in Afghanistan, Ryan mentioned a Janesville friend who has been deployed there. When the topic was Medicare, Ryan talked about what the health care program for seniors had meant for his mom, and how Social Security benefits helped him and her when his father died when he was a teenager.
He defended the GOP proposals on Medicare. "We are not going to jeopardize this program, but we have to save it," Ryan said.
Biden responded with apparent disbelief. "Folks, use your common sense," he said, looking straight into the camera. On this issue, he asked, "who do you trust?
Sitting at a small curved table on a red-carpeted stage, both seemed to have learned one particular lesson from last week's debate, when Obama drew ridicule for repeatedly taking notes rather than looking at his opponent. Each occasionally jotted a note but both took care to watch the other and address them, face to face.
The first striking thing about their standoff was how different the two men were. The second: how much they were the same.
The differences were obvious, starting with the generational contrast. Biden is 69 years old, a member of the so-called Silent Generation that came before the Baby Boomers. Wisconsin Congressman Ryan is 42, the first member of post-Boomer Generation X to be nominated by a major party on a national ticket.
The disparity in their ages was the widest of any national debate in the television age much bigger than the 17-year age gap between Ronald Reagan and Walter Mondale in 1984, more than double the divide between Dick Cheney and John Edwards in 2004, a tad bigger than the one between Bentsen and Quayle.
Then there are their politics. Biden is one of the nation's senior Democrats, beloved by many of the blue-collar and Jewish voters who help make up the party's liberal base. Ryan is an up-and-coming Republican with a more reliably conservative history than running mate Mitt Romney and a stronger appetite for stirring controversy, especially on budget issues. That has made him a favorite of the Tea Party movement.
Those differences were spotlighted on stage at Centre College in the sole debate between them, sandwiched between the first and second debates between the men at the top of the tickets.
But the similarities between Biden and Ryan also shaped their conversation, from their common roots in blue-collar America to long political careers that made each congressional royalty. In those ways, they resemble one another more than they do the presidential nominees.
Both are Catholics born in manufacturing towns in the Rust Belt that have seen economic struggles Biden in Scranton, Pa., and Ryan in Janesville, Wis. and that continue to shape the ways they relate to voters and the stories they tell on the campaign stump. Each is better at connecting with blue-collar workers from swing states than their presidential partners.
The running mates' political careers are remarkably similar, though a generation apart.
Both were interested in elected office from the start. Biden won his first election to the New Castle County Council in Delaware at age 28. At 28, Ryan also won his first election, to represent Wisconsin's 1st Congressional District.
Biden stayed in the Senate for seven terms, including a tenure as chairman of the Senate Foreign Relations Committee, before becoming vice president. Ryan has served seven terms in the House and chairs the budget committee. The congressional experience sometimes showed. Biden, for instance, kept referring to Ryan as "my friend."
But he didn't seem to mean it.