Hillary Clinton (AFP/Getty Images)

Democrats really want Hillary Clinton to run for president in 2016 -- and it's as much about how much they like her as about how she appears to be, far and away, their best shot at keeping the White House. Most polls, in fact, show her retaining a double-digit lead over whomever the GOP nominates.

That owes in large part to the popularity she  retains from a well-received turn as secretary of state.

But if history is any guide, that popularity will disappear right about the moment she launches a 2016 presidential campaign, rendering her just as polarizing a politician as she used to be. Indeed, the idea that Clinton will continue to post a big lead on whomever the GOP puts up is pretty far-fetched.

Polls in recent decades show us that basically every time a well-known national figure launches a campaign for president, they quickly see their numbers take a turn for the worse.

Here's Al Gore (D), who was a relatively popular vice president before running in his own right in 2000, according to Gallup polling. He stayed in positive territory through most of the 2000 campaign, but he dipped underwater at the end with a 46 percent favorable rating and a 52 percent unfavorable rating:


And here's Bob Dole (R), who was quite well-known and well-liked as a war hero, former presidential candidate and Senate majority leader heading into his 1996 campaign. By mid-1995, he was another politician with a middling favorable rating:

It happened to a lesser extent to another war hero-turned-presidential candidate, John McCain (R). McCain was also a well-known national figure and former presidential candidate when he entered the 2008 race as the GOP frontrunner.

He quickly fell back to earth during the GOP primaries, but like Dole saw his numbers rebound quite nicely during the general election:

The common thread between Gore, Dole and McCain, of course, is that they all lost, despite entering their campaigns with good personal image numbers and nationwide appeal.

The best example of the challenge ahead for Clinton, though, is Clinton herself. She has gone through this cycle twice now.

She was quite popular during the latter end of her tenure as first lady, peaking at a 67 percent favorable rating as the calendar turned to 1999. Then, during her 2000 New York Senate campaign, it dropped as low as 45 percent.

During much of her tenure in the Senate, her national favorable rating rebounded into the mid-to-high 50s. In 2007, though, after launching her presidential campaign, it quickly dropped to right around 50-50 again and stayed there until her campaign was over.

Hillary fave

In fact, we're already seeing the same thing happen well in advance of 2016 or even 2015. As Clinton's potential 2016 candidacy continues to be a focal point of the media -- and as Republicans continue to press the case on her handling of Benghazi -- we've already seen her numbers head south.

Polls have shown her favorable rating, which again peaked right around two-thirds favorable during her tenure as secretary of state, already dropping into the 50s and, in one poll last month, to 49 percent.

She's still running ahead of the GOP competition, but at this point, that's probably equal parts a function of her popularity as a function of her being much better-known than her potential GOP opponents.

And if history is any guide, she would probably return to right around 50-50 once the campaign began in earnest.