Vice President Joe Biden has already run for president twice (in 1988 and 2008). And during inaugural festivities over the last several days, he ignited a fresh round of speculation that he's going to give it one more try in 2016. On Saturday, the gaffe-prone veep told the crowd at the Iowa State Society Inaugural Ball that he was "proud to be president of the United States." He later courted leaders from other early primary states — New Hampshire and South Carolina — to hear him take the oath of office at the Naval Observatory and be sworn in by Supreme Court Justice Sonia Sotomayor, the third woman and first Latina to issue the oath. Indeed, many analysts say Biden's presidential prospects have never been better. Others aren't so sure. Here, four reasons Biden might go down in flames if he makes a bid to succeed President Obama:

1. He's too old

"To be blunt, he's old," say Mike Allen, Jonathan Martin, and Jim Vandehei at Politico. Biden is 70 now and would be 74 if he ran and won," which would make him the oldest person ever to assume the job. "He's also old news in politics. The guy has been in Washington for almost two generations and hardly signals freshness or political vitality."

2. He could never beat Hillary Clinton

Biden's popularity is high, says Taegan Goddard's Political Wire, but outgoing Secretary of State Hillary Clinton's is significantly higher. Clinton's favorability rating is 67 percent, according to a new ABC News/Washington Post poll, compared with 48 percent for Biden. The bottom line, says Ken Thomas at The Huffington Post, is that Clinton is the "heavy favorite" in the Democratic primaries against Biden or anybody else. If she runs, he's toast. His only chance is if Clinton decides not to run again, and that's a pretty big "if."

3. He can't beat the top Republican hopeful

No Democrat, Hillary Clinton included, can match the best the GOP has to offer, and that's Sen. Marco Rubio of Florida, says Matt K. Lewis at The Week. Rubio isn't a contender because he's a Washington insider who waited his turn. He has "the vision, charisma, brains, and communications skills to fix the problems that will no doubt linger long after Obama has returned to Chicago." That's why, watching President Obama taking the oath of office, "I couldn't help thinking that four years from now, it'll probably be President-elect Marco Rubio's turn."

4. He's no Barack Obama

Biden has his pluses, says Jason Howerton at The Blaze. As Obama's two-time vice president, he has plenty of Democratic stalwarts on his side. He also has a well-known "ability to connect with regular folks," and years of campaign experience. "But he would also need to deal with personal poll numbers that rank below Obama's and a propensity to commit foot-in-mouth moments in an era where political gaffes can quickly sink a campaign." It's hard to imagine Joe Biden as president, says Dusten Carlson at The Inquisitr. He's more like "the weird uncle you avoid at Thanksgiving of the Democratic Party. He's as "gaffe-worthy as Mitt Romney" and "as off-putting as Ron Paul." But unless the GOP can start producing better contenders of its own, we might all want to "start practicing the words 'President Biden,'" just in case.