HELENA, Mont. — He might not have been their first choice, but Republicans are all in on Montana's Matt Rosendale as they look to defeat Democratic U.S. Sen. Jon Tester, the incumbent who has drawn President Donald Trump's ire.

State party leaders, national Republicans and conservative donors began rallying around the state auditor and insurance commissioner Wednesday, a day after he won a heated GOP Senate primary. Rosendale said he received a congratulatory call from Donald Trump Jr. and that he hopes the president will campaign with him in Montana during the general election.

Rosendale, 57, will be relying on that party unity, continued help from deep-pocketed GOP donors and the president's support as he takes on a two-term incumbent who has already raised more than $12 million before the Nov. 6 campaign has even begun. Tester has a little more than half that amount in the bank.

Outsiders from both sides will be trying to influence the race, Rosendale said.

"I think there's a big difference between the people supporting me and supporting him," he said. "They want to restore control, that decision-making process, back to the people of Montana."

Tester campaign manager Christie Roberts said Rosendale is funded by special interests and would be bad for public lands, veterans and health care.

Rosendale, a former real estate developer and state lawmaker, is an unlikely challenger to Tester, whom Trump has attacked for releasing misconduct allegations that derailed his nominee to head the U.S. Department of Veterans Affairs.

Montana GOP leaders originally considered former U.S. Rep. Ryan Zinke their best shot at defeating the farmer from the town of Big Sandy, but Zinke dashed their hopes when he became Trump's Interior Department secretary in early 2017.

Party leaders received another setback when popular Attorney General Tim Fox later announced he wouldn't run for Senate. That created the opportunity for Rosendale, who stepped in not long after winning his first statewide election as auditor two years ago.

"When Secretary Zinke was selected to serve as the Interior secretary, absolutely it changed a lot of the political landscape in Montana," Rosendale said Wednesday. "But the people spoke last night, and I have earned their support over the years."

Voters have been favoring Republican candidates for statewide office since 2010, and party leaders hope Trump's landslide win in Montana two years ago will provide momentum to Rosendale this year.

Plus, Tester has never won a majority of the vote in his previous Senate victories, and this year's race will include a Libertarian Party candidate and possibly a Green Party candidate who could siphon Democratic votes.

The state Democratic Party is suing to challenge the Green Party's eligibility for the ballot.

Rosendale and his family moved from Maryland to Montana in 2002 after buying a ranch near the town of Glendive. He ran for the state Legislature and won in 2010 as Republicans took control of the state House.

He was elected as a state senator two years later and became Senate majority leader in 2015.

Rosendale's first run for federal office came in 2014, when he lost to Zinke in the GOP primary for Montana's U.S. House seat. He won the state auditor's office in 2016 amid another Republican wave in which the party took three of four statewide offices from Democrats.

He was one of four candidates in Tuesday's GOP Senate primary and became the early favorite of national Republican donors and groups that poured $3 million into the race to support him.

Retired Judge Russ Fagg attacked Rosendale in hopes of chipping away at his front-runner status, calling him a "weak candidate" and political opportunist seeking his fifth elected office in eight years.

Fagg also said out-of-state groups were trying to buy the election for Rosendale, calling him an East Coaster with different values from Montana residents. He said Wednesday that he will support Rosendale.

"Campaigns are a contact sport, but once it's over with, I think we can pull together," Fagg said.

Tester's campaign and Montana Democrats have co-opted many of Fagg's attacks, dubbing Rosendale "Maryland Matt" and accusing him of being propped up by special interests.

"There is no greater contrast for Montana voters this November than a third-generation dirt farmer from Big Sandy and an East Coast real estate developer who's just not right for Montana," Tester campaign spokesman Chris Meagher said.

Rosendale was dismissive of the attacks.

"It demonstrates to me how little they have to run on," he said.