Republican businessman Tim Sheehy has defeated incumbent Democratic Sen. Jon Tester in Montana's U.S. Senate race, Scripps News and Decision Desk HQ project.

Sheehy's win means Republicans have flipped at least three previously Democratic-held seats, giving the GOP a majority in the next session of Congress. Tester had held the seat in the generally Republican-leaning state since 2007.

Tester had won relatively competitive elections in 2006, 2012 and 2018 before getting upended by Sheehy on Tuesday.

This race has also been among the most expensive in the U.S., according to Open Secrets. Tester, however, had a massive advantage in donations over Sheehy. But Sheehy entered Tuesday with a slight advantage in the polls.

Tester had in some ways tried to distance himself from President Joe Biden. He was among the first Democratic members of the Senate to call on Biden to exit the presidential race. He tried to paint himself as a bipartisan member of Congress.

But Sheehy tried to tie Tester to Biden and Vice President Kamala Harris in a state that overwhelmingly voted to support former President Donald Trump.

With Sheehy's win, Republicans are projected to have at least 52 out of 100 seats in 2025. Races in Pennsylvania, Michigan, Nevada and Arizona remain uncalled.