Nobody really knows whether Vice President Biden will run, but there's a debate in Democratic circles about whether he can afford to wait. Chip Somodevilla/Getty Images hide caption

itoggle caption Chip Somodevilla/Getty Images

Supporters of Democratic presidential candidate Hillary Clinton cheer as she arrives at the state's annual Democratic convention Saturday in Manchester, N.H. Jim Cole/AP hide caption

itoggle caption Jim Cole/AP

A man carries a cardboard cutout of Hillary Clinton in Des Moines, Iowa. Clinton and other traditional candidates have struggled to breakthrough as outsiders have captured the attention this summer. Charlie Neibergall/AP hide caption

itoggle caption Charlie Neibergall/AP

Hillary Clinton speaks at the Democratic National Committee's summer meeting in Minneapolis, where she was trying to court all-important party delegates to her side. Jim Mone/AP hide caption

itoggle caption Jim Mone/AP

President Obama has stayed neutral in the race to replace him, but as rumors swirl that Vice President Biden could jump in, a White House spokesman said Monday it's possible Obama will endorse. Saul Loeb/AFP/Getty Images hide caption

itoggle caption Saul Loeb/AFP/Getty Images

Sen. Ted Cruz, R-Texas, apologized Wednesday after making a joke about Joe Biden while the vice president was mourning the death of his son. Charles Dharapak/Associated Press hide caption

itoggle caption Charles Dharapak/Associated Press

Vice President Biden and House Speaker John Boehner wait for President Obama's State of the Union address in front of a joint session of Congress in 2012. As vice president, Biden is also leader of the U.S. Senate, but only gets a vote when senators are evenly divided. Saul Loeb/AP hide caption

itoggle caption Saul Loeb/AP

Vice President Joe Biden was criticized for coming up from behind and getting too close to Stephanie Carter at her husband's swearing-in ceremony as secretary of defense. Evan Vucci/AP hide caption

itoggle caption Evan Vucci/AP

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