Sen. Kelly Ayotte (R-N.H.) testifies during a Senate Judiciary Committee hearing on Jan. 27, 2016. (Alex Brandon/AP)

Sen. Kelly Ayotte (R-N.H.) is trailing her Democratic rival, Gov. Maggie Hassan, by 10 points in what has been one of the tightest Senate races in the country, according to a new poll from WBUR Radio.

The poll, which was conducted between July 19 and Aug. 1, shows 50 percent of respondents saying they would vote for Hassan if the election were held today, compared with 40 percent for Ayotte. Ayotte is one of the most vulnerable GOP senators up for reelection in a year in which Republicans can afford to lose only three seats if they hope to maintain control of the Senate.

The boost for Hassan also mirrors the surging popularity of Democratic presidential nominee Hillary Clinton in New Hampshire. Clinton leads Republican presidential nominee Donald Trump 47 to 32 in the state, according to the same poll. Her favorability rating also climbed to 45 percent from 35 percent in May. Meanwhile, Trump’s favorability fell from 33 to 29 percent.

Democrats were happy to blame Trump for Ayotte’s decline. Ayotte has long said she will vote for the GOP nominee, despite criticizing Trump for his feud with the parents of Army Capt. Humayun Khan, who was killed in Iraq in 2004. Trump responded by bashing her as a weak and disloyal leader, comments that have not dissuaded Ayotte from backing him, according to aides.

“It’s clear that Ayotte’s decision to support Trump for president — and to continue to stand by him as he reinforces every day just how temperamentally unfit he is to serve as president — is hurting Ayotte’s standing with New Hampshire voters,” said Aaron Jacobs, a spokesman for Hassan’s campaign.

Aides to Ayotte declined to comment.

Hassan is also leading Ayotte in favorability, particularly among independents and women. Hassan’s overall favorability is at 50 percent, with 32 percent of voters viewing her unfavorably. Ayotte’s favorability is at 42 percent with 32 percent unfavorability. Hassan’s favorability among women is at 53 percent and 50 percent among independents. Ayotte trails by more than 10 points in each category — 38 percent among women and 36 percent among independents.

The race has grown increasingly negative as Ayotte seeks to retain her seat for a second term. Outside groups have poured money into attack ads on everything from Hassan’s handling of an opioid addiction crisis that has swept the state to Ayotte’s record of votes against abortion rights.

Ayotte has also been attacked from the right as she prepares for a Sept. 13 primary in which she will face four Republican opponents. She is widely expected to win and go on to face Hassan in November, but conservatives have used the opportunity to frame her as an out-of-touch Washington insider.

The poll reached 609 likely New Hampshire voters between July 29 to Aug. 1 through calls to land lines and cellphones. The margin of error is four percentage points.