Bullock won three statewide elections in Montana prior to this year, all while the state voted for Republicans for president. He was seen as a rare Democrat — possibly the only one in 2020 — capable of separating Daines’ reelection race enough from the presidential race to put the seat at risk of flipping.

Senate Leadership Fund, the Republican super PAC, took the unusual step of launching ads against Bullock while he was still running for president, just in case he ended up switching into the Senate race later.

Daines, who was elected to the Senate in a landslide in 2014 after serving one term as Montana’s lone House representative, has reliably backed President Donald Trump in the Senate, including voting to repeal the Affordable Care Act that allowed Bullock to extend Medicaid. Daines has also been one of Congress’ most aggressive voices against Chinese trade practices and foreign policy.

But during the campaign Daines also emphasized bipartisan policies such as an environmental conservation law Trump signed this year that was popular in the state. On his health care positions, Daines said it was “highly unlikely” the Supreme Court would nix the Affordable Care Act and added he backed coverage for patients with preexisting conditions, though he didn’t offer details for how.

Daines also cast Bullock as aligned with the Democratic Party’s liberal wing on gun control and suggested Bullock’s environmental views would limit the state’s coal-mining industry.

Bullock championed his bipartisan accomplishments in two terms as governor, including working with a Republican-led legislature to expand Medicaid. When he ran for president last year, Bullock backed raising the federal minimum wage to $15 per hour, increasing paid leave, instituting universal background checks for gun purchases, banning assault weapons and limiting dark money in politics.

David Lim contributed to this report.