Age.

Biden will be 73 in 2016. He’ll turn 74 12 days after Election Day, which would make him the oldest newly elected president to take the oath of office if he were to win in 2016. Reporters have described Biden as “spry,” “smiling,” and “jolly,” in articles about his age as a way of suggesting he could handle the rigors of office. This is not a new issue for voters to grapple with. In 2008, when the prospect of John McCain swearing the oath of office at 72 was a real possibility, nearly half of Americans surveyed in a CNN/ORC poll saw age as a factor. Forty-seven percent worried McCain wouldn’t finish his first term.

The Hillary roadblock.

One very real obstacle stands in the way of a potential Biden campaign: Hillary Rodham Clinton. She is very popular among Democratic voters, so much so that she leads a field of Democrats with 65 percent supporting her, according to a new Quinnipiac University poll released this week. Biden is the next closest potential competitor, but lagging far behind 13 percent. She’s got institutional advantages: A super PAC, Ready for Hillary, is already working on her behalf. This week EMILY’s List launched a campaign to elect a woman as president. We do not know if Hillary is going to run, but we are hopeful that she will,” EMILY’s List President Stephanie Schriock said.