U.S. President Barack Obama and Vice President Joe Biden walk back to the Oval Office on June 25, 2015. (REUTERS/Jonathan Ernst)

Vice President Joe Biden, rumor has it, is considering running in 2016 with an asterisk: If elected, he'd pledge to serve only one term.

"[O]ne thing that I keep hearing about Biden is that if he were to declare and say, because age is such a problem for him if he does, I want to be a one-term president," Carl Bernstein (perhaps you've heard of him?) told CNN on Friday.

Biden is 72 years old and would be 78 upon completing his first term. That's five years older than the oldest president to be sworn in for a second term -- Ronald Reagan, at 73. Which, we'll note, is how old Hillary Clinton would be at her second inauguration.

So how about that! A pledge to only serve one term. Who could imagine such a thing?

Well, lots of people, actually.

First, we'll note that there's already a 2016 candidate that has pledged to serve one term: the fabled 18th Republican candidate, Mark Everson. Everson's decision to make his pledge a prominent aspect of his campaign doesn't seem to have done much, to date.

Second, we'll note that dangling a one-term pledge as a differentiator is a gambit as old as the Republic itself -- or very nearly.

The historic one-termers

Three American presidents made -- and kept -- pledges to serve one term at most. Rutherford B. Hayes and James K. Polk made one-term pledges; each served one term. William Henry Harrison, our second-oldest president at 68, also took a pledge to serve only one term, a pledge that was in keeping with his Whig Party. That pledge turned out not to matter; he barely served a full month before dying.

(An excerpt from a letter written by James Watson Webb, a prominent Whig politician.)

The Franklin Roosevelt backlash one-termers

One-term pledges gained some popularity in the early 1940s, as well, as Franklin Roosevelt was in the middle of his unprecedented four-term electoral winning streak. Before the 1940 election, Republican Sen. Arthur Vandenberg of Michigan suggested that his party should adopt a one-term limit for its nominee. Vandenberg ran to be that nominee; he came in fourth.

Four years later, New Hampshire Sen. Styles Bridges (R) made a similar proposal. Bridges didn't run, but the issue became unimportant a few years later with the adoption of the 22nd Amendment, limiting presidents to two terms.

The gimmicky one-termers

Before that amendment, a pledge to restrict how long you'd serve actually made a little sense. You could, after all, be reelected until you died, as Roosevelt did. But after the amendment? Making a pledge to limit to one term instead of two seems awfully gimmicky.

In 2008, John McCain -- trailing in most polls -- flirted with the idea, but decided against it, in part for the reason that Biden might embrace it: it would draw attention to his age. In 1996, Bob Dole similarly considered a one-term pledge, in part as an attempt to entice Colin Powell to join his ticket. Run as Dole's VP, the pitch went, and the field would be clear in 2000 for a Powell presidential run.

Needless to say, that didn't happen either.

The humblebrag one-termers

There's a variant on the one-term pledge that bears mentioning. Call it the "humblebrag pledge": That a candidate would be so fervent in his push for his party's ideals or for "getting things done" that he or she would essentially sacrifice any chance of being reelected.

Sen. Rob Portman of Ohio suggested that Mitt Romney would be a humblebrag one-termer in 2012. Michele Bachmann, in that election's primaries, was more explicit: "I'm also committed to being a one-term president if that's what it takes in order to turn things around, because this is not about a personal ambition," she said, according to the Des Moines Register. Such nobility!

The pundit one-termers

Then there's another category: The I'm-a-pundit-and-I-recommend-the-one-term-pledge-gimmick one-termer.

Hillary Clinton should pledge to serve only one term!, Roger Simon wrote in 2014.

John McCain should pledge to serve only one term!, Walter Shapiro and Ramesh Ponnuru wrote in 2008.

Are there more examples? Probably. Is Bernstein's Biden speculation one of them? It's hard to say. He's hearing that this is what Biden is thinking. But then, on Thursday afternoon, we were hearing that Al Gore might run, thanks to "people."

The real question, though, is whether or not such a pledge would actually do any good. If someone made the pledge and then got elected, would they hold to it? A number of congressional candidates during and since the 1994 wave election made term-limit pledges -- and a number of them have broken them. Once president, it seems hard to think a politician would simply walk away.

Or, put another way:

'Oh, you're enjoying my presidency? Then let's just stay, shall we?'

Correction: This article originally said McCain ran for president in 2012, because I am tired. It was 2008, of course.