Newark Mayor Cory Booker said Thursday that he won't, under any circumstances, run for president in 2016. “Absolutely yes, unequivocally,” Booker told Politico's Maggie Haberman when asked whether he would rule out seeking the nation's top office or accepting the vice presidential nomination in 2016.

Cory Booker isn't running for president in 2016. Or might he? (Reuters)

Done and done. Take Booker's name off of lists like ours that rank the top potential contenders for the 2016 presidential nomination. (We had Booker ranked as the fifth most likely nominee in our most recent update.)

Or not. A quick look back in history shows any number of candidates who said they absolutely wouldn't run for president only to reconsider later.

The most famous example is, of course, the current occupant of the White House who flatly told NBC's Tim Russert in January 2006 he would not run for president in 2008. "I will serve out my full six-year term," Obama said. "You know, Tim, if you get asked enough, sooner or later you get weary and you start looking for new ways of saying things, but my thinking has not changed.'

By November 2006, Obama was back on "Meet the Press" saying something very different. "Well, the—that was how I was thinking at that time," Obama explained. "And, and, you know, I don’t want to be coy about this, given the responses that I’ve been getting over the last several months, I have thought about the possibility."

Two years later, he was elected president.

In Booker's home state of New Jersey, Gov. Chris Christie spent much of 2011 denying any interest in running for president in 2012, and insisting that the media was looking for a story where there wasn't one.

But then, in the fall of 2011, Christie confirmed he was re-considering his past denials of interest. (And, as Dan Balz's book details, Christie was heavily wooed to change his mind by some of the heaviest hitters within the party.)  Christie ultimately decided, again, not to run.

The point of this stroll through recent history is that a politician ruling out a run for president three years before the actual race happens can't be taken as a definitive statement. Circumstances change. And, as Obama's election in 2008 proved, voters don't really hold past statement of disinterest in running against you.

(Side note: The only people who pay attention to these sorts of pronouncements about races that are several years away are political junkies. And, as we have established many times, we are not the average person.)

Which brings us back to Booker. We take him at his word that today, with his election to the Senate in a fall special election still not a totally done deal, that he has no interest or plan to run for president in 2016.

But, times change.  Assuming Booker gets elected to the Senate -- and he is a heavy favorite -- you can be certain that he will immediately come under pressure to begin, privately, re-assessing his pledge not to run.

As we have written before, if Massachusetts Gov. Deval Patrick takes a pass on 2016, there will be no other prominent African-American politician even being mentioned in the presidential primary discussion. Given Obama's success in a crowded 2008 primary, it's hard to imagine that Booker wouldn't, at the very least, have to consider running if Patrick didn't. (That statement is 100 percent true if Hillary Clinton stays out of the race; if she runs, it's possible that all normal calculations politicians like Booker make go out the window.)

Booker says "no" today  -- and he means it. But politics is a fungible business.  Just ask Barack Obama.