Rep. Mike Coffman of Colorado was the first Republican in Congress last year to cut an ad promising to “stand up” to Donald Trump — and six months into the presidency, he has tried to live up to that promise, bucking the president on immigration, health care and other issues.
As Republicans try to defend their House majority next year, lawmakers like Mr. Coffman are trying to find that elusive middle between being a Republican and being a Trump Republican.
For Mr. Coffman, who said last year that he “didn’t care for [Mr. Trump] much,” little has changed. He is vowing to keep bucking the president when he wants, including voting against the American Health Care Act and trying to chart a more lenient path for illegal immigrants.
“Mike Coffman has a long track record of independent leadership — challenging big spenders in both parties and putting the interests of his constituents first. As Mike has said before, he will stand with President Trump when he agrees with him and stand up to him when he thinks he’s wrong,” said Tyler Sandberg, campaign adviser to Mr. Coffman.
Mr. Coffman won his district by 9 percentage points last cycle — in the same region where Democratic presidential nominee Hillary Clinton topped Mr. Trump by 9 points.
Some Republicans say that’s a good sign: Voters are willing to split their ticket and reward congressional Republicans even if they do not support Mr. Trump. One party strategist said that if incumbents such as Mr. Coffman can win swing districts when Mrs. Clinton or Barack Obama is on the ballot, then they are strong enough to win midterm elections.
Others said that might not be the case next year.
“The Republican majority could not be any worse than it is right now,” said David Flaherty, CEO of Magellan Strategies in Colorado. He said Republicans like Mr. Coffman will need to switch up their campaign strategies now that Mr. Trump is in the White House, and they can no longer sell themselves to voters as checks on government.
Instead, it’s Democrats who will be able to portray themselves as checks on a runaway Republican Party.
The “generic ballot test” — when voters are asked if they would vote for a Democrat or a Republican in their district’s congressional election next year — is tilting toward Democrats by 9 percentage points, according to Real Clear Politics’ average of polls.
Mr. Coffman is one of nearly two dozen Republicans representing districts Mrs. Clinton won last year.
Another is Rep. Barbara Comstock, Virginia Republican, whose district stretches from the Shenandoah Valley to the Washington suburbs. Ms. Comstock won her district in November by 6 points, and Mrs. Clinton won it by 10 points.
Mr. Coffman and Ms. Comstock voted against Republicans’ American Health Care Act and have voiced criticism of Mr. Trump’s other policies.
“I did not support the AHCA today because of the many uncertainties in achieving those goals. As the process moves forward, I hope that we can continue to work together to fix our broken health care system,” Ms. Comstock said in a statement after the May vote.
Democrats, though, said each lawmaker has plenty of votes to gut Obamacare that they will have to explain.
“Coffman is extremely vulnerable in 2018, especially in a district that was carried by Hillary Clinton and has seen an explosion of civic activism,” Morgan Carroll, chairwoman of the Colorado Democratic Party, said in a statement.
Democrats also said opposing Mr. Trump on some high-profile issues isn’t enough for voters who want to see a broader resistance.
“Congresswoman Comstock is stuck between a rock and a hard place,” said Cole Leiter, a spokesman for the Democratic Congressional Campaign Committee. “She can pretend to be a moderate and isolate herself from her base voters or march lockstep with her party and confirm for families who have rejected the Trump-Washington Republican agenda who she really is. It’s an untenable position.”
Ms. Comstock has voted for Mr. Trump’s position 97 percent of the time, according to FiveThirtyEight’s count. Mr. Coffman’s record is slightly less lockstep but still at 94 percent.
Nathaniel Gonzales, editor of Inside Elections, said Republicans are still looking for that elusive spot that shows independence but doesn’t alienate Trump supporters.
“I think every Republican member is playing a game of ‘Survivor’ and trying to get the right equation to get re-elected. Barbara Comstock tried to distance from the president, but she also needs voters who like the president,” Mr. Gonzales said.
Early polling suggests competing influences at work. A Washington Post/ABC News poll last month found a slight majority of voters — 52 percent — want Democrats to take control of Congress next year, but Republicans and Trump voters are more enthusiastic about their candidates.
Democrats say they have much better odds than Republicans because of Mr. Trump’s historically low approval ratings and because the party in power usually loses some seats in midterm elections.
“Republicans are in a race to the right to see who can be the Trumpiest candidate. Voters in Colorado understand that a vote for the Republican Party in 2018 is a vote for the Trump agenda of giving more tax breaks to millionaires and billionaires and then sticking middle-class and working families with the bill,” Ms. Carroll said.