When Sen. Jon Tester, a Montana Democrat, vouched for President Trump’s pick to be the new interior secretary, there was perhaps more than a little self-interest involved.
Rep. Ryan K. Zinke, a Republican and the administration’s secretary nominee, had been expected to challenge Mr. Tester in next year’s Senate race.
Now, with Mr. Tester’s backing, Mr. Zinke is likely to leave Congress and join the administration, leaving behind a much thinner Republican bench in the state — and giving Mr. Tester a little more job security.
Given the Democrat’s voting record, he may need more of a margin for error next year.
Mr. Tester has tacked to the left, opposing Republicans and voting against Mr. Trump’s nominees more than any other Democrat in a deep-red state — one that went for Mr. Trump by 20 percent in November.
“I think the biggest question is who the heck is going to run against him among Republicans because everyone thought Zinke was going to run,” said David C.W. Parker, a political science professor at Montana State University.
As Republicans look at the Senate map in 2018, Mr. Tester is a target. He won his 2006 and 2012 races by narrow margins, with just 49 percent support each time.
Political handicappers rank Mr. Tester in the second tier of likely Republican pickups, putting him in a slightly stronger position than Democratic Sens. Joe Donnelly of Indiana, Claire McCaskill of Missouri, Heidi Heitkamp of North Dakota and Joe Manchin III of West Virginia, who are viewed as being on shakier ground.
Still, his seat should be considered in play, analysts said.
“He will be a tough incumbent, but Trump’s performance was strong enough that at least one or two people will take the leap,” said Nathan L. Gonzales, of Inside Elections, a nonpartisan group that tracks campaigns.
Mr. Gonzales said Republicans “could end up with a better candidate than Ryan Zinke.”
“On the one hand is a member of Congress who has been elected statewide, but that also makes him a member of Congress and part of Washington and an extremely unpopular chamber,” he said. “So whoever Republicans get, we at least know they are not going to be tied directly to Congress.”
Republicans sound confident that Mr. Tester can be toppled.
“Jon Tester is part of the most extreme version of the Democratic Party in Washington, who want to fight President Trump at every turn,” said Katie Martin, of the National Republican Senatorial Campaign Committee. “The Washington liberal elite refuses to work to get things done, and Jon Tester is going to have to explain to hardworking Montana voters why he is a part of the problem.”
The Democratic Senatorial Campaign Committee did not respond to multiple inquiries seeking comment.
Mr. Tester dismissed the idea that Mr. Trump’s performance spells doom for him.
“Look, Montanans are known for splitting tickets. It is not a concern,” he said.
Asked whether Mr. Trump lingers in the back of his mind during votes, Mr. Tester said bluntly, “Nope, never, never.”
Indeed, while other embattled Democrats have tried to show their bipartisan credentials under Mr. Trump, bucking party leaders to back some congressional Republican or Trump priorities, Mr. Tester has more often sided with Democrats’ liberal wing.
Last week, he split with the four most embattled Democrats by voting against a Republican-sponsored measure that scrapped a proposed rule aimed at preventing coal-mining debris from getting into streams.
He also voted against confirming Rex Tillerson as secretary of state because of concerns over his ties to Russia and voted against Rep. Mike Pompeo’s nomination to lead the CIA because of concerns that the Kansas Republican wants to “revive and expand some of the worst elements of the Patriot Act,” including re-establishing bulk metadata collection.
“This type of bulk data collection Mr. Pompeo advocates for fails to protect our right to privacy and potentially treats innocent Americans like hostile actors,” he said.
The senator from Montana also sided with the Senate’s most liberal Democrats to try to block retired Marine Gen. James Mattis from being eligible to run the Defense Department — though in the end he, along with most of the rest of those Democrats, did vote to confirm Mr. Mattis.
But Mr. Tester also has irked progressive groups by refusing to bow to demands that lawmakers dismiss Supreme Court nominee Judge Neil Gorsuch, and suggesting that he and Mr. Trump are on the same page when it comes to reducing regulations.
The ranking member of the Senate Veterans’ Affairs Committee, Mr. Tester has also called on Mr. Trump to shield military veterans from his 90-day federal hiring freeze.
• Seth McLaughlin can be reached at smclaughlin@washingtontimes.com.
Please read our comment policy before commenting.