DOTHAN, Ala. — Heading into the midterm elections, President Trump has become a one-man litmus test in some of his party’s primaries, imperiling incumbents in races where policy issues seem to matter less to voters than personal loyalty to the president.
Perhaps nowhere has this been seen more acutely than in Alabama’s Second Congressional District, where Republican voters face a peculiar choice in a runoff: A congresswoman who condemned Mr. Trump but has since voted nearly in lock step with him, or a challenger who was once a Democrat who supported Nancy Pelosi, but now sounds much like the president.
“It’s like a lot of elections: Which is the best of a bad choice?” said Brandon Shoupe, a Republican and county commissioner in southeast Alabama who has not endorsed either the incumbent, Martha Roby, or her runoff rival, Bobby Bright. “You’ve got an unpo[CENSORED]r flavor of Republican currently holding the office, and then you’ve got a former Democrat that’s running.”
But the unusual pairing barely fazed many Republican voters. Indeed, Linda Lane-Overton, who lives in Alabama’s Wiregrass region, said she had comfortably arrived at a two-part test for making her decision.
“We have to look at both candidates and feel sure that our vote will be for the candidate that can win the election in November — and be loyal to our president,” she said on Thursday.
The fact that an incumbent like Ms. Roby has been forced into a runoff by questions of personal fealty illustrates the potency of the issue in this year’s Republican primaries. Another test of just how dangerous it can be for a Republican lawmaker to cross Mr. Trump looms on Tuesday.
Republican voters in a South Carolina district will decide whether they want to nominate Representative Mark Sanford for another term or replace him with Katie Arrington, a state lawmaker who has made Mr. Sanford’s criticisms of the president the centerpiece of her insurgent campaign.
Mr. Sanford has spent nearly $400,000 on advertising in recent months to try to hold on to his Charleston-based district, airing a commercial in which he says, “Overwhelmingly, I’ve voted with the president.”
“We’re at an interesting inflection point in American politics,” he said in an interview. “If somehow dissent from your own party becomes viewed as a bad thing, then we’re not really vetting and challenging ideas in the way the founding fathers intended.”
Broadening his argument, Mr. Sanford said America was meant to be “a nation of laws, not men” and that “we weren’t a cult of personality.”
Mr. Sanford said he recognizes that Republicans in his district, which Mr. Trump carried by 14 points, want him to line up with the president, and cited a survey saying that he had voted with Mr. Trump in Congress 89 percent of the time. “I love my brother and sister, but I don’t agree with them 89 percent of the time,” he said.
Still, his opponent, Ms. Arrington, has made extensive use of clips of Mr. Sanford taking aim at Mr. Trump. She argued in a debate this month that “our first job is to listen to the captain” and that “Mark Sanford has spent the better part of two years bashing our captain.”
Ms. Roby, by contrast, has not staked out a position of anything approaching regular dissent; she essentially opposed Mr. Trump in public only for a short period near the end of the 2016 presidential campaign, over his personal behavior. After a recording surfaced of Mr. Trump making vulgar comments about women, she said he was “unacceptable as a candidate for president” and urged him to step aside.
“When she came out against Trump, the people down here in this part of the state — oh my God, they hate it,” said Will Matthews, a Republican lawyer in Ozark. “She showed her true colors to kowtow to the traditional Republican Party people.”
On Election Day, Mr. Trump easily carried the Second District, but Ms. Roby won re-election with only 49 percent of the vote; two years earlier, she had taken about two-thirds.
Things only seem to have gotten worse for her since then. Facing better prepared opposition than the last-minute write-in campaign her critics mounted in 2016, Ms. Roby managed to attract just 39 percent of the vote in the five-way Republican primary last week, necessitating a runoff on July 17.
Her primary performance, dismal for a four-term incumbent, stemmed from a political reality of the Trump era: Republican primaries often draw voters with enormous, and largely unquestioning, affection for the president.
Recognizing that reality, Republican candidates for the United States Senate in Mississippi have been jockeying over who is the most faithful to Mr. Trump — a striking echo of a Senate race last year in Alabama.
Ms. Roby’s district, covering all or part of 15 counties, was ripe for just such a contest, with voters scattered from Montgomery’s northern suburbs down Highway 231 toward the peanut farms around Dothan, near the Florida border. Indeed, the danger for Ms. Roby, especially in a part of the Second District known for its conservatism as well as the texture of its grass, was clear almost immediately after she questioned Mr. Trump’s fitness.