Hillary Clinton has opened a 15-point lead on Donald Trump in New Hampshire, after trailing Trump by 2 points there in May.

The new WBUR/MassINC poll said Clinton is ahead 47-32, a huge swing from Trump's 44-42 lead in May. The Libertarian Party's Gary Johnson polled at 8 points, while the Green Party's Jill Stein earned 3 points in the latest poll.

Compared to the May poll, Clinton's unfavorable rating dropped 13 points, from 58 to 45, while Trump's unfavorable rating rose 2 points, from 58 to 60.

When Johnson and Stein were removed from the poll and Trump and Clinton squared off one-on-one, Clinton's lead expanded to 17 points, 51-34.

The result show voters are worried about Trump's fitness to lead the country. Sixty-three percent of those surveyed said he was not "fit" to be president, compared to 31 percent of respondents who believed he was fit.

Clinton, however, was not underwater by the same metric. Forty-eight percent of New Hampshire respondents said she was "fit" to be president, while 46 percent of voters said she was not fit.

Since the end of the conventions, Trump's support appears to have cratered in the Granite State. RealClearPolitics' average of polling leading into the convention showed Clinton up single-digit percentage points, with an average lead of less than 4 points. Trump's 15-point deficit represents a stark departure from previous polling there.

The GOP nominee is counting on New Hampshire, and said earlier this week that he was doing "very well" in New Hampshire and was performing better than incumbent GOP Sen. Kelly Ayotte in the polls.

The latest New Hampshire poll also spells bad news for Ayotte, who's in a tough re-election battle with the state's sitting Democratic governor, Maggie Hassan. The governor holds a 10 percentage point lead, 50-40 over Ayotte.

The WBUR/MassINC survey of 609 likely voters was conducted July 29-August 1 by landline and cellphones. The poll has a 4 point margin of error.

The timing of the poll suggests New Hampshire voters were swayed by the conventions. Seventy-one percent of respondents said they watched the Democratic convention while 68 percent of survey respondents said they watched the GOP convention.

A majority of New Hampshire voters, 56 percentage points, said they thought Clinton came out of the Democratic convention looking stronger. Just 39 percent of respondents thought Trump appeared stronger after the convention ended.