What's driving Hillary's rebound?

After spending the summer polling just ahead of her chief rival, Vermont Sen. Bernie Sanders, polls now show Hillary Clinton surging ahead.

If summer was one long slump for Hillary Clinton, autumn seems to be a fresh start. 

Two new polls show the Democratic presidential candidate staging a strong rebound. Some 54 percent of registered Democrats support Mrs. Clinton, up 12 points from one month ago, according to an ABC News/Washington Post poll out Tuesday. 

Clinton's lead over her rival, Vermont Sen. Bernie Sanders, has also surged, from 7 points in September to 20 points this month, according to an NBC News/Wall Street Journal poll that was also released Tuesday. 

Why, after months of controversy over her use of a private e-mail server while serving as secretary of State, as well as her handling of the deaths of Americans at the US consulate in Benghazi, Libya, does Clinton appear to be making a comeback? 

"This isn’t entirely unexpected for people who have been watching the polls and looking at the fundamentals of the campaign," says Frank Orlando, a political scientist at Saint Leo University in Saint Leo, Fla. 

"When you are the frontrunner you are going to get heat – from Republicans and Democrats alike. Clinton has gone through a period in the campaign where she has undergone a great amount of scrutiny, and some of this was self inflicted. Clinton’s numbers swooned a bit," but the polls aren't always perfect reflectors of what's happening in a race, Professor Orlando adds. 

For starters, many are crediting Clinton's performance in last week's Democratic presidential debate for her resurgence. Some 45 percent of Democrats and those leaning Democratic said they thought she won the debate, as opposed to 19 percent who said Senator Sanders won, according to the ABC News/Washington Post poll. 

Her campaign has also credited its "campaign reset," an effort to show Clinton's warmth, humor, and personality, as one reason behind her rebound. 

And it doesn't hurt that most voters continue to see Clinton as the inevitable Democratic nominee. According to the ABC News poll, two-thirds of Democrats and Democratic-leaning independents say they expect her to win the nomination. 

Following their summer crushes (on Sanders, mostly), Democratic voters are returning to Clinton, says Jonathan Rothermel, a professor of political science at Mansfield University in Mansfield, Penn. 

“Before the presidential race started to heat up, the presumed top candidates were always Hillary Clinton and Jeb Bush – the establishment candidates," Professor Rothermel said.

"However, primaries introduce voters to other prospective candidates, and voters have a tendency to flirt with the idea of a non-establishment candidate.... [But] voters are beginning to shift their thinking to electability mode." 

Don't forget that despite Sanders's rise and the looming threat of a Joe Biden candidacy, Clinton continues to perform best among women and minorities. She's also got high support – 63 percent – among voters who stress the importance of experience, a department in which Clinton excels. 

"Because of these established advantages, Clinton will be favorite no matter what the flavor of the week was in the Democratic Party," says Orlando. 

It's not smooth sailing for Clinton from here on out, though. According to the ABC News poll, Clinton is still vulnerable on her perceived lack of honesty and trustworthiness.

And Vice President Biden entering the race would change the political calculus. 

That said, according to some political observers, Clinton didn't actually rebound – she's always been a strong candidate, despite the narrative voters may have heard from the media or the polls. As the blog FiveThirtyEight recently pointed out, she's enjoyed near-unanimous support from the Democratic establishment, high favorability ratings among Democrats, a solid lead in national polls, and frankly, relatively weak opposition. 

"From our vantage point, then, declaring a “Clinton comeback” is a bit like declaring Tom Brady or LeBron James to be the comeback player of the year," writes Nate Silver of FiveThirtyEight. "Clinton didn’t have anything to come back from; she was winning the nomination race before last night’s debate — by a lot."