Editor's note: David Gergen is a senior political analyst for CNN and has been an adviser to four presidents. A graduate of Harvard Law School, he is a professor of public service and director of the Center for Public Leadership at Harvard University's Kennedy School of Government. Follow him on Twitter.
(CNN) -- What a difference two debates have made.
Before the first presidential debate last week, President Barack Obama appeared to be cruising toward re-election and possibly a thumping victory. After the first presidential debate, that changed dramatically: Suddenly, we had a horse race. Now after the vice presidential debate Thursday night, we not only have a horse race, but partisans fired up on both sides.
Joe Biden relit the fire under Democrats in a passionate, often dominant tangle with Paul Ryan. Going into that encounter, Democratic spirits were not only drooping but some were beginning to panic that they were throwing away the election.
Biden put a forceful stop to the caterwauling -- or, as Gloria Borger put it, righted the ship. He was especially effective in countering Ryan on Medicare and (as Van Jones argued after the debate) in making a case that a Romney administration could mean the end of Roe v. Wade. An old pro, Biden knows how to play to seniors, women and the middle class.
But Republicans took equal encouragement from Ryan's performance. And well they should. Ryan was a steady, unflappable presence onstage who made an articulate set of arguments in favor of conservative principles while also seeming sensitive and reasonable to many moderates. Ryan was also surprisingly strong on foreign policy, holding his own against a man far more schooled in the subject. Overall, he more than justified Mitt Romney's judgment in choosing him as running mate.
On substance, I called it a draw right after the debate (as did Wolf Blitzer and a few others on our CNN team). That was good news for both Biden and Ryan. The latter could claim credit for being one of the only two challengers who has ever fought a sitting vice president to at least a draw, the first being Al Gore against incumbent Dan Quayle in 1992.
The CNN poll of registered voters who had watched the debate reached a similar conclusion: Forty-eight percent said Ryan won, 44% said Biden, though the difference was within the poll's margin of error. A CNN focus group thought it was a draw as well. (Note to candidates: What the focus group liked most was when Biden and Ryan said what their administrations would do to fix the economy. Could we possibly hear more of that in the remaining presidential debates?)
But there was another element to the debate that has aroused more controversy. As it did in the first presidential debate, CNN chose to show the two candidates on a split screen throughout the evening. (Good call). Watching that, I found Biden's frequent laughs at Ryan to be off-putting -- and indeed, condescending. That plus the interruptions were in stark contrast to Ryan's calm, even-keeled performance. So on style, I thought the edge went to Ryan.
As often happens in these highly charged times, many Democrats sharply disagreed with that judgment on Twitter. They thought I along with some colleagues were jackasses (that is a very polite rephrasing of their language). Many cited a CBS poll after the election that found Biden a clear overall winner.
What was lost in translation is that the CBS poll was of uncommitted voters and the CNN poll of all registered voters. Recognizing there can be honest differences, I stand by my call -- Biden was overbearing in the early part of the debate and that diminished the impact of his arguments.
Taken altogether, the vice presidential debate did make a difference: Biden was able to help his boss out of the hole -- he helped to stabilize the race. But Ryan was able to keep the GOP fired up, too. Both campaigns now gallop forward, looking toward the next showdown this coming Tuesday night when CNN's Candy Crowley is the moderator. It's a close horse race with passions high, fans on their feet.
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The opinions expressed in this commentary are solely those of David Gergen.