U.S. Vice President Joe Biden, right, and Republican vice presidential candidate Paul Ryan depart the stage following their debate on Thursday, October 11. See the many expressions of Vice President Joe Biden during the debate. 
President Barack Obama watches the vice presidential debate aboard Air Force One with staff while heading home from Florida on Thursday. 
Vice President Joe Biden and U.S. Rep. Paul Ryan walk off stage after the vice presidential debate. 
Vice presidential candidate Ryan greets family following his debate with Vice President Biden. 
Vice President Joe Biden and Rep. Paul Ryan mingle with their families after the debate. 
Vice President Biden smiles during the debate. 
Rep. Paul Ryan listens closely during the debate. 
Vice President Biden and vice presidential candidate U.S. Rep. Ryan go head to head in the first and only vice presidential debate. 
Vice President Biden reacts to comments made during the debate. 
Vice presidential candidate Ryan lays out his views. 
Vice President Biden responds to points made. 
Vice presidential candidate Paul Ryan engages the moderator during the vice presidential debate. 
U.S. Vice President Joe Biden, left, engages in the first and only vice presidential debate on Thursday, October 11. 
Vice President Biden reacts during the debate. 
Vice President Biden and vice presidential candidate Paul Ryan face off. 
Vice President Biden greets Republican vice presidential candidate Paul Ryan as they take the stage. 
Vice President Joe Biden speaks during the vice presidential debate as moderator Martha Raddatz looks on. 
Vice President Biden, left, and Republican vice presidential candidate Ryan, right, participate in the debate. 
Ryan speaks during the debate. 
Biden presents his views on Thursday. 
Ryan awaits his turn to speak. 
Vice President Joe Biden, left, shakes hands with Republican vice presidential candidate Paul Ryan before the vice presidential debate. 
Janna Ryan, wife of Paul Ryan, waves to the crowd. 
Dr. Jill Biden, wife of Joe Biden, greets the crowd. 
An audience member holds a debate program. 
Debate moderator Martha Raddatz speaks to the crowd prior to the start of the vice presidential Debate. 
- David Gergen: Two debates in two weeks have transformed presidential race
- Gergen says the polls have tightened, partisans on both sides are fired up
- CNN poll gave a slight edge to Paul Ryan; Gergen says he had edge on style
- Gergen: Tuesday's town hall debate looks increasingly important
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.
Amusing moments during VP debate 
Ryan: Romney cares about 100% 
Biden, Ryan argue over Bush tax cuts 
Ryan, Biden get personal on abortion 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.
