According to a new WBUR poll of New Hampshire voters, Hillary Clinton is enjoying a dramatic post-convention bump and now leads Donald Trump by 15 points. Our poll also shows Democrat Maggie Hassan with a big advantage in her bid to unseat Republican Sen. Kelly Ayotte.

Democrats Unite Around Clinton

The last time we polled in New Hampshire, three months ago, the presidential contest was virtually tied. Our new poll (topline, crosstabs) of 609 likely New Hampshire voters, conducted July 29 through Aug. 1, shows Clinton leading Trump 47 percent to 32 percent. When Libertarian Gary Johnson and Green Party candidate Jill Stein are omitted, Clinton's 15-point lead swells to 17 points.

Among the most important reasons Clinton has moved ahead so dramatically in this important swing state following last week's Democratic National Convention is that Democrats are uniting around her.

"After all the hand-wringing about whether Bernie Sanders supporters would end up supporting Hillary Clinton, she's now getting 86 percent of the Democratic vote," explained Steve Koczela, president of the MassINC Polling Group, which conducted the WBUR survey. "Donald Trump, on the other hand, has slipped a bit among Republicans. He's now getting a bit less than two-thirds of the Republican vote."

Another big factor: The state's many undeclared voters favor Clinton over Trump by almost 2-1.

"Digging underneath that even further we see independent women is where the biggest margin of all is among groups that are actually in play," Koczela said. "So when you add it all together, Clinton has solidified Democrats, Donald Trump has not done the same among Republicans, and independents are starting to swing toward Hillary Clinton."

Fit To Be President?

Post-convention polls can show big swings before settling down. But the WBUR poll suggests a dramatic development in a state where Trump won a decisive victory in the primary last February, and where Clinton was trounced by her opponent, Bernie Sanders.

The WBUR survey found that 48 percent of likely voters say Clinton is fit to be president, 46 percent say she's not. But with regard to Trump, less than a third say he's qualified to occupy the White House and more than 60 percent say he's not.

Selena Katz, an elementary school teacher in Keene, is among that majority.

"It would be, I think, disaster to have him as president," Katz said.

When asked whether her vote is for Clinton or against Trump, Katz says it's for Clinton. "I feel that she's very experienced, she's very knowledgeable, very rational, and because she works with other people in a cooperative manner — that's what we need as our president."

It appears that in New Hampshire, Clinton got a substantially bigger bump from her convention than Trump did from his. The WBUR poll found that about the same number of people watched both conventions, but 56 percent said that Clinton emerged stronger, compared to 39 percent who said Trump did.

Katz, the teacher, says the conventions reinforced her pro-Clinton view. And she says Trump's post-convention criticism of the Khan family, whose Muslim-American son died fighting in Iraq, solidified her negative view of the Republican nominee.

"When he talked about what his sacrifices were, they were all business dealings," Katz said. "They had nothing to do with the loss of a child serving in the military to defend the United States."

Less than 30 percent of New Hampshire voters view Trump favorably. Sixty percent view him unfavorably. He's a bit more unpopular today than he was three months ago, when WBUR conducted its last New Hampshire poll.

Clinton, on the other hand, has improved somewhat on this score — but she's still far from beloved: 45 percent have a positive view of her, but the same percentage of voters have a negative view. So there are still lots of people in New Hampshire ready to vote against her.

Among them is Bill Lauer, a Republican who owns a small farm in Swanzey. He's voting for Trump.

"I do not want to see Hillary get in — at all costs," he said. "Because Hillary Clinton is going to basically continue the agenda of the current administration."

Lauer represents another key finding in our poll: He's among the large majority of New Hampshire voters who think the U.S. and the world are much less safe today than in recent years. So he's drawn to Trump as the "law and order candidate." But Lauer says Trump's criticism of the Khan family went too far — and he says sometimes he'd like to tell his candidate to just "shut up."

"A lot of his advisers have told him that in the past, and he goes on to do and say whatever he wants. He'll get away with it. Ultimately, the people that are standing by Trump, and the people that will vote for Trump, are voting for, ultimately, they're voting for change," Lauer said. "And that's what's going to get him elected."

N.H. Senate Race Feeling Impact Of Presidential Contest

The WBUR poll also found the presidential contest is having a big effect on New Hampshire's Senate race between the incumbent Republican, Kelly Ayotte, and the Democrat, Gov. Maggie Hassan. According to the poll, Hassan now leads by 10 points in a race that could determine which party will control the Senate.

In a race that could determine which party controls the Senate, our new poll shows that New Hampshire Gov. Maggie Hassan, a Democrat, is leading incumbent Republican Sen. Kelly Ayotte by 10 points. (AP file photos)

"There's a very close relationship between the votes for Kelly Ayotte and Donald Trump," pollster Koczela said. "Their support is sort of locked together. And with the direction that Donald Trump seems to be heading in, Kelly Ayotte's task is to somehow decouple those two."

That has proved difficult for Ayotte, who has put herself in the awkward position of not explicitly endorsing Trump, while saying she will support the Republican nominee in November.

Over the weekend, in a rebuke to Trump, Ayotte defended the Khan family — which prompted the Republican nominee to lash out at her.

"I don’t know Kelly Ayotte," Trump told the Washington Post. "I know she’s given me no support — zero support — and yet I’m leading her in the polls. I’m doing very well in New Hampshire."

This latest poll suggests otherwise — and that, at least for now, New Hampshire poses a challenge to both Trump and Ayotte.