One of the many lessons Barack Obama taught the political world was that time spent in Washington was inversely proportional to your chances of winning a presidential election.

At the start of the 2008 campaign, Obama had to face down a series of questions -- mostly from a political press based here in Washington -- about whether someone who had spent just two years (at the time) in the U.S. Senate was qualified to be president.  Obama addressed these lingering questions in the formal announcement of his campaign in Springfield, Ill., in 2007. Said Obama: "I know I haven't spent a lot of time learning the ways of Washington. But I've been there long enough to know that the ways of Washington must change."

Turns out he was right — and he's getting more right with every passing year. Check out this chart courtesy of the Pews Research Center:

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And, it's actually worse than it looks for politicians with "Washington" on their résumé. Just 19 percent said having served in Washington would make them more likely to support a candidate for president while 30 percent said it would make them less likely to back said candidate.  Compare that to the 33 percent who said that having been a governor makes them more likely to support a candidate and you see the problem for politicians with scads of D.C. experience. (People were six times as likely to say that having served in Washington would be a negative for them as they were of gubernatorial service. Six times!)

The numbers — in terms of who tends to win presidencies — strongly favors governors, too. Obama was the first senator to be elected to the nation's top office since John F. Kennedy, way back in 1960.  A governor -- or former governor -- has been the GOP nominee in three of the past four elections.  Democrats had quite a run with governors from 1976 to 1996 (with apologies to Michael Dukakis).

The Pew numbers should be of interest to anyone wondering how the 2016 presidential campaign might play out.  Democrats seem ready to nominate Hillary Rodham Clinton, who spent the past two-plus decades in Washington — as a senator and the nation's top diplomat. By contrast, a number of potential Republican 2016ers — Jeb Bush, Scott Walker, Chris Christie, John Kasich, Bobby Jindal — are either current or former governors.  "Republicans will still be biased towards a governor with accomplishments to be our nominee," said Charlie Spies, a Republican lawyer and strategist. "For the 40 percent of Americans [who] still think Obama is doing a good job, then young and charismatic may be enough, but in a Republican primary the Obama analogy may prove perilous."

What the Pew data — as well as scads of real-world cases make clear: If Clinton winds up as the Democratic nominee, one of her main challenges will be convincing a skeptical public that her time spent in Washington isn't such a bad thing. And that's a gigantic change from when she and her husband first entered the national political game.