The vice president, who was on the presidential campaign trail last year in Florida, spent Tuesday calling winning candidates across the country. Matt Rourke/AP hide caption

itoggle caption Matt Rourke/AP

Then-Secretary of State Hillary Clinton and Vice President Biden at a White House event in October 2011. A new book says President Obama's aides were then studying whether to replace Biden with the former first lady on the 2012 ticket. Kevin Dietsch /UPI /Landov hide caption

itoggle caption Kevin Dietsch /UPI /Landov

Vice President Biden earlier this month during a roundtable discussion on gun control at Girard College in Philadelphia. Tim Shaffer /Reuters /Landov hide caption

itoggle caption Tim Shaffer /Reuters /Landov

Vice President Joe Biden leads the first meeting of the working group to explore solutions following the Newtown shooting with Philadelphia Police Commissioner Charles Ramsey and other law enforcement leaders on Dec. 20. Chip Somodevilla/Getty Images hide caption

itoggle caption Chip Somodevilla/Getty Images

"No, this really is Joe Biden!" (He borrowed a Costco employee's phone to say hello to someone.) Saul Loeb /AFP/Getty Images hide caption

itoggle caption Saul Loeb /AFP/Getty Images

Vice President Biden and his Republican opponent, Rep. Paul Ryan of Wisconsin, participate in the vice presidential debate at Centre College in Danville, Ky., Thursday. Charlie Neibergall/AP hide caption

itoggle caption Charlie Neibergall/AP

Sen. Lloyd Bentsen (D-Texas) shakes hands with Sen. Dan Quayle (R-Ind.) before their vice presidential debate at the Omaha Civic Auditorium in Omaha, Neb., on Oct. 5, 1988. Ron Edmonds/AP hide caption

itoggle caption Ron Edmonds/AP

Rep. Paul Ryan greets supporters during a campaign rally Sunday in Waukesha, Wis. Saul Loeb/AFP/Getty Images hide caption

itoggle caption Saul Loeb/AFP/Getty Images