More than three in five young Americans prefer that a Democrat win the White House in 2016 rather than a Republican. And Vermont Sen. Bernie Sanders is alone among the five major presidential hopefuls still in the race who has a net positive favorability rating.

Those are two of the findings in a new survey of American adults under 30 years old by Harvard University's Institute of Politics at the John F. Kennedy School of Government.

Sixty-one percent of 18-to-29 year-olds prefer that a Democrat be elected president in the fall, while 33 percent of those surveyed back a Republican. That gap of 28 percentage points has nearly doubled since a similar poll conducted last year, when the difference was just 15 percentage points with Democrats again in the majority.

In a hypothetical head-to-head contest among likely voters, Democrat Hillary Clinton trounces Republican Donald Trump, 61 percent to 25 percent — a 36-point margin. Of those likely voters surveyed, 14 percent said they were undecided.

The poll found that millennials largely reject Trump, the leading Republican candidate. He has the highest negative ratings of any of the candidates included in the survey: 74 percent have an unfavorable view of Trump compared with 17 percent who have a favorable view of the billionaire businessman. Among millennials who identify as Republican, Trump's numbers remain 20 points underwater in terms of favorability (37 percent positive to 57 percent negative).

Trump's GOP rivals, by comparison, are viewed positively by the young Republicans polled: 39 percent favorable, 27 percent unfavorable for Ohio Gov. John Kasich; 56 percent favorable, 30 percent unfavorable for Texas Sen. Ted Cruz.

Among millennials overall, a minority 37 percent view Clinton favorably; 53 percent view her unfavorably. Among millennials who identify as Democrats, 65 percent view her favorably and 30 percent unfavorably.

Perhaps not a surprise given his ability to draw large, predominantly young crowds to rallies, Sanders is by far the most popular of the five presidential candidates included in the Harvard poll. In fact, with 54 percent viewing him favorably and just 31 percent unfavorably, he's the only candidate in the survey who has a positive net favorable number.

"I think what's striking about this is, when we look at young voters who view Bernie Sanders very favorably, Clinton actually has 80 percent of that vote," John Della Volpe, the director of the Harvard Institute of Politics poll, told reporters in a conference call Monday.

In a Trump-Clinton match-up, Trump would receive 69 percent of those who rate Cruz very favorably. Trump receives 42 percent of Kasich supporters. But 30 percent of Kasich supporters would vote for Clinton against Trump.

"Clinton seems to be doing a better job coalescing young Democrats, while Donald Trump has had trouble coalescing young people on the right," Della Volpe said.

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