Republicans could lose the Senate. And they’d have Donald Trump to blame.

The biggest worry for Republicans isn’t that Donald Trump will lose. It’s that he’ll lose so badly that he’ll end up dragging down GOP candidates in other races, costing the party the Senate and maybe the House.

Lately it looks like those fears might come true. A new WBUR poll in New Hampshire shows Trump down 15 points to Hillary Clinton in the state. But more significantly, Republican Sen. Kelly Ayotte is down 10 points in her bid for reelection against Maggie Hassan, the former Democratic governor.

For Republicans, this is an important race, and could be a key to Senate control. Democrats currently hold 46 seats and need to take just four from Republican incumbents to take back the Senate if Clinton wins (and five if she does not).

To be clear, this is just one poll, and it could be driven by a Democratic convention bounce that will fade over the next few weeks. But it highlights an important dynamic in the election: When Trump’s campaign starts going “off the rails,“ as it has in recent days, other Republicans get dragged down with him:

“There’s a very close relationship between the votes for Kelly Ayotte and Donald Trump,” said Steve Koczela, president of the MassINC Polling Group, which conducted the WBUR survey. “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.”

Lately, Ayotte has tried to disavow Trump’s attacks on Khizr and Ghazala Khan. In a recent statement, she said:

The Khan family deserves nothing less than our deepest support, respect, and gratitude, and they have every right to express themselves in any way they choose. I am appalled that Donald Trump would disparage them and that he had the gall to compare his own sacrifices to those of a Gold Star family.

But separating herself entirely from Trump will be difficult. Though she hasn’t endorsed Trump, Ayotte’s aides say she still backs him (à la her famous “support, but not endorse” statement) and plans to vote for the Republican presidential nominee.

One saving grace for Ayotte may be the fact that Trump has been distancing himself from her. In a recent interview with the Washington Post, Trump didn’t sound like he would endorse or support Ayotte.

I don’t know Kelly Ayotte. 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. We need loyal people in this country. We need fighters in this country. We don’t need weak people. We have enough of them. We need fighters in this country. But Kelly Ayotte has given me zero support, and I’m doing great in New Hampshire.

A rift with Trump could arguably be a good thing for Ayotte. Another option might be to do what Sen. Mark Kirk (R-IL) did — last month he revoked his support for Trump and became the first Republican senator to run an anti-Trump ad. According to a Kirk campaign official, Kirk has seen “an uptick in donor and volunteer interest since the senator distanced himself from Trump.”