Control of the Senate appears likely to flip from the Democratic Party to the Republican Party this fall, as one of the nation’s most endangered Democrats, Sen. Jon Tester of Montana, trails his Republican challenger in his bid for reelection, according to a new poll from The New York Times and Siena College.

Tester is winning over moderate and independent voters and running far ahead of the Democrat at the top of the ticket, Vice President Kamala Harris. But that does not appear to be enough to survive in Montana, where former President Donald Trump is ahead by 17 percentage points and where control of the Senate hangs in the balance.

Tim Sheehy, a wealthy Republican businessperson and a former Navy SEAL who has never held public office, leads Tester 52% to 44%, the poll shows. Sheehy’s lead is a 7-point advantage without rounding.

Democrats currently hold a 51-seat Senate majority. But with Republicans already set to pick up a seat after the retirement of Sen. Joe Manchin, I-W.Va., who caucuses with Democrats, the party cannot afford to lose additional seats.

In fact, the party’s only hope is to secure a 50-50 split and to have Harris win the White House, allowing her running mate, Gov. Tim Walz of Minnesota, to provide the crucial tiebreaking vote as vice president.

At least seven other Democratic-held Senate seats are competitive this fall, including in the presidential battlegrounds of Arizona, Michigan, Pennsylvania, Nevada and Wisconsin. In late September, a series of Times/Siena surveys in four of those races, as well as in Ohio, found Democrats ahead, though narrowly in some cases.

The problem is that the Democratic Party has scarce opportunities to flip any Republican-held seats in 2024 to make up for any potential losses, such as in Montana.

This year, Republicans are hoping to make the Senate race in Montana a national partisan referendum. In the poll, 55% of likely voters said they would prefer that Republicans control the Senate, compared with only 37% who prefer Democratic control.