Will Joe Biden run for president in 2016?

In an interview that aired on CNN on Sunday, Vice President Joe Biden left the door open to running for president in 2016 - he said he'd "make up my mind on that later" - and suggested he was physically and mentally prepared for the challenge.

"I'm in one of the -- probably the best shape I've been in my life," said Biden. "I'm doing pretty well. I'm enjoying what I'm doing. And as long as I do, I'm going to continue to do it."

If he runs and wins in 2016, Biden would be 73 years old when he took office. His age would be an issue for the electorate - he would be the oldest incoming president in U.S. history - but perhaps not a disqualifying one.

There are two recent instructive examples: 2008 Republican presidential candidate John McCain, who would have been 72 years old when he took office. While McCain's age (and previous health issues) generated some concern, the issue never overshadowed his candidacy. Then there's former president Ronald Reagan, who was reelected in 1984 at the age of 73. Reagan is the most admired Republican president in recent history, but there is continued debate over whether he began suffering the symptoms of Alzheimer's disease before he left office.

Age isn't Biden's only potential roadblock: Based on his two past presidential runs, it's not clear that the Delaware native would be a particularly strong candidate. Biden's lack of discipline in public comments can cause headaches for his staff, as when he suggested in early 2007 that then-candidate Obama was "the first mainstream African-American who is articulate and bright and clean and a nice-looking guy" to seek the presidency. Biden's loose lips haven't been a significant problem for the Obama administration - his characterization of health care reform as a "big f***ing deal" ultimately went over pretty well - but his off-the-cuff style means he is more likely than most presidential candidates to sink his bid with one ill-considered remark.

And then there's Biden the campaigner. During his 2008 presidential run, I got to see Biden's famed long-windedness up close. At town hall sessions, you'd watch seniors politely trying to stifle their yawns as Biden gave overly detailed, digressive answers (many lasting more than 10 minutes) to relatively simple questions. The crowds in Iowa seemed to like Biden personally, but his style simply didn't galvanize primary voters; he finished fifth in the caucuses, with just one percent of delegates, and was out of the race soon after. (His 1988 run is somewhat less instructive, in large part because it was overtaken by a plagiarism scandal.)

Biden would likely come into the 2016 race with a tailwind, thanks to his high-profile perch if Mr. Obama wins re-election. In the year 2000, Al Gore - who is, to put it nicely, no one's idea of a charismatic campaigner - managed to win his party's nomination (and nearly take the presidency) after eight years as former President Bill Clinton's vice president. George H.W. Bush did the same thing in 1988 after eight years under Mr. Reagan. If Mr. Obama wins a second term, it will be particularly tempting for Biden to try to follow suit.

And depending on the state of the nation's economy in four years, he could potentially be the right candidate for the moment. Biden connects particularly well with blue collar audiences, and while the former senator spent his career as a politically moderate Washington insider, he could plausibly mount a populist campaign similar to the one run by John Edwards in 2008. Indeed, Biden is arguably better at connecting to working class Americans than his boss, whose oratorical skills sometimes spill over into the professorial; for the labor unions that play a significant role in Democratic politics, Biden could make an appealing standard bearer.

The 2016 campaign is still a long way away, of course. Four years from now, Biden may not want to undertake the rigors of a presidential campaign. But he has shown more than once that he has presidential ambitions, and unlike Secretary of State Hillary Clinton, his political appetite shows no sign of diminishing. If Mr. Obama wins re-election, he'll have another profile-enhancing four years in the public eye and a good chance at appropriating the massive fundraising network developed by the president. In light of all that, it isn't easy to imagine a man who has served in Washington since 1973 simply walking away.