Vice President Joe Biden speaks during the vice presidential debate with Republican vice presidential nominee Rep. Paul Ryan, of Wisconsin. (AP Photo/David Goldman)
Vice President Joe Biden and Republican vice presidential nominee Rep. Paul Ryan of Wisconsin spar during the vice presidential debate. (AP Photo/Charlie Neibergall)
Jill Biden, center, wife of Vice President Joe Biden, sits with her sons Beau Biden, left, and Hunter Biden, right, before the start of the vice presidential debate, at Centre College in Danville, Ky. (AP Photo/Pablo Martinez Monsivais)
Vice President Joe Biden and Republican vice presidential nominee Rep. Paul Ryan of Wisconsin participate in the vice presidential debate. (AP Photo/Pool-Michael Reynolds)
Republican vice presidential nominee Rep. Paul Ryan, of Wisconsin, right, watches as Vice President Joe Biden, speaks during the vice presidential debate. (AP Photo/David Goldman)
Moderator Martha Raddatz watches as Vice President Joe Biden and Republican vice presidential nominee Rep. Paul Ryan of Wisconsin shake hands before the vice presidential debate. (AP Photo/Pool-Michael Reynolds)
Moderator Martha Raddatz, left, reaches across to greet Republican vice presidential candidate, Rep. Paul Ryan, R-Wis., right, as Vice President Joe Biden, center, takes his seat for the start of the vice presidential debate. (AP Photo/Pablo Martinez Monsivais)
Vice President Joe Biden and Republican vice presidential candidate, Rep. Paul Ryan, R-Wis., shake hands before the start of the vice presidential debate. (AP Photo/Pablo Martinez Monsivais)
Bert Christian of Louisville, Ky., carries a sign in support of Vice President Joe Biden ahead of the vice presidential debate between Biden and Republican vice presidential candidate, Rep. Paul Ryan, R-Wis.,. (AP Photo/David Goldman)
Shadows are cast across the floor as people pass by outside the debate hall ahead of the vice presidential debate with Republican vice presidential candidate, Rep. Paul Ryan, R-Wis., and Vice President Joe Biden, Thursday, Oct. 11, 2012, at Centre College in Danville, Ky. (AP Photo/David Goldman)
Vice President Joe Biden, left, and Republican vice presidential nominee, Rep. Paul Ryan, of Wisconsin, challenge each other during the vice presidential debate Thursday, Oct. 11, 2012, at Centre College in Danville, Ky. (AP Photo/Eric Gay)
Vice President Joe Biden and Republican vice presidential nominee Rep. Paul Ryan of Wisconsin participate in the vice presidential debate at Centre College, Thursday, Oct. 11, 2012, in Danville, Ky. (AP Photo/Pool-Rick Wilking)
Vice President Joe Biden and Republican vice presidential nominee Rep. Paul Ryan of Wisconsin participate in the vice presidential debate at Centre College, Thursday, Oct. 11, 2012, in Danville, Ky. (AP Photo/Pool-Rick Wilking)
Vice President Joe Biden and Republican vice presidential nominee Rep. Paul Ryan of Wisconsin participate in the vice presidential debate at Centre College, Thursday, Oct. 11, 2012, in Danville, Ky. (AP Photo/Pool-Rick Wilking)
A sign promoting the vice presidential debate is held up at a rally on the Centre College campus, site of the debate, Thursday, Oct. 11, 2012, in Danville, Ky. Vice President Joe Biden will face Republican vice presidential candidate, Rep. Paul Ryan, R-Wis. (AP Photo/Eric Gay)
Chris Herron of Danville, Ky., has his picture taken Oct. 11, 2012, with a cutout of President Obama outside the Norton Center on the Centre College campus in Danville, Ky., where the debate between Vice President Joe Biden and Republican vice presidential candidate Paul Ryan was to take place later that day. (Associated Press)