HELENA — Ryan Zinke was the Republican Party’s first choice to take on incumbent Democratic Sen. Jon Tester in 2018 and re-claim the seat that would give Montana an all-GOP congressional delegation.

President Donald Trump dashed those hopes by snatching the former congressman to become his interior secretary.

“I fully expected that Zinke would be the guy,” GOP chairman Jeff Essmann said Tuesday. “My world was blown up.”

With Greg Gianforte saying he’ll seek to stay in Montana’s only U.S. House seat, the field of potential challengers to Tester is narrowing.

Republicans in Montana and in Washington, D.C., are now courting the state’s attorney general, Tim Fox, to step up and run against Tester next year. Fox is a popular incumbent who won re-election with 67 percent of the vote last year.

Fox was recently U.S. Sen. Steve Daines’ guest for Trump’s joint congressional address. While he was in Washington, Fox said he met Trump, Zinke, Vice President Mike Pence and Attorney General Jeff Sessions, among others.

Fox didn’t rule out a run against Tester next year but said his main concern now is making sure his office’s budget and bills move through the legislative session.

“A lot of people asked me about the 2018 election,” Fox said. “I appreciate people wanting to talk about this, it’s important for the people in our state. It’s not my priority at the moment.”

Re-taking Tester’s Senate seat has been a long-coveted prize for the GOP since the bristle-haired farmer from Big Sandy upset former Sen. Conrad Burns in the 2006 election.

Former U.S. Rep. Denny Rehberg came close in 2012, losing to Tester by 18,072 votes after a long, bruising campaign. The Republican Party sees 2018 as an opportunity to pick off Tester by riding the momentum of wins in the 2016 election, including Trump capturing 55 percent of the vote in Montana.

With Zinke out of the picture, Gianforte was seen as a possible challenger to Tester. The Bozeman businessman lost to incumbent Democratic Gov. Steve Bullock in his first run for public office last year, but he built name recognition after spending millions of dollars on ads and trekked across the state to meet voters.

Gianforte could still challenge Tester, but his entry in this year’s race to serve the remainder of Zinke’s term in the U.S. House complicates matters. Gianforte told The Associated Press last week that if he wins the May 25 special election, then he will seek to retain the House seat in the 2018 election.

That leaves open the possibility that Gianforte could run for governor again in 2020, but it would eliminate him as a contender for U.S. Senate.

Other potential Republican candidates include some or all of those who won Montana’s statewide offices last November. One of them, State Auditor Matthew Rosendale, said he had not made a decision about the 2018 race.

“We’ve got plenty of time to talk about the next campaign cycle,” Rosendale said.

The 2018 election is 20 months away. Rehberg launched his campaign 21 months before the 2012 election — and still lost.

Tester is already ramping up his re-election campaign. He’s hired a campaign manager and is meeting with voters and raising money. He had $1.5 million in campaign cash on hand at the end of last year.

Campaign manager Christie Roberts said in a statement that Tester’s record as a senator makes him a formidable candidate.

“We look forward to stacking that record up against anybody,” she said.