THE WOODLANDS, Texas — Representative Dan Crenshaw was tagged as a rising Republican star almost from the moment of his first victory: A conservative, Harvard-educated, ex-Navy SEAL who lost his right eye in Afghanistan, he bucked the 2018 suburban revolt against Donald J. Trump to win a House seat in the Houston suburbs.

Mr. Crenshaw won again in 2020, handily, even as Mr. Trump carried his district by only a whisper.

But this year, Mr. Crenshaw’s seat has been transformed by redistricting. More liberal enclaves, like the nightlife-rich neighborhoods near Rice University, were swapped out for conservative strongholds like The Woodlands, a master-planned community of more than 100,000 that is north of the city.

The result: Mr. Trump would have carried the new seat in a landslide.

The new lines mean Mr. Crenshaw now has a vanishingly slim chance of losing to a Democrat in the next decade. The only political threat would have to come from the far right — which, as it happens, is already agitating against him.

All across the nation, political mapmakers have erected similarly impenetrable partisan fortresses through the once-in-a-decade redrawing of America’s congressional lines. Texas, which holds the nation’s first primaries on Tuesday, is an especially extreme example of how competition between the two parties has been systemically erased. Nearly 90 percent of the next House could be occupied by lawmakers who, like Mr. Crenshaw, face almost no threat of losing a general election, a precipitous drop that dramatically changes the political incentives and pressures they confront.

“What the future of the Republican Party should be is people who can make better arguments than the left,” Mr. Crenshaw said in an interview. Yet in his new district, he will only need to make arguments to voters on the right, and the farther right.

When primaries are the only campaigns that count, candidates are often punished for compromise. The already polarized parties are pulled even farther apart. Governance becomes harder.

The dynamic can be seen playing out vividly in and around Mr. Crenshaw’s district. He appears in no imminent political danger. He faces underfunded opposition in Tuesday’s primary, out-raising rivals by more than 100 to one.

But his repeated rebuke of those who have spread the falsehood that Mr. Trump won the 2020 election — fellow Republicans whom he has called “performance artists” and “grifters” capitalizing on “lie after lie after lie” — have made him a target of what he derisively termed “the cancel culture of the right.”

“They view me as a threat because I don’t really toe the line,” Mr. Crenshaw said.

He has especially sparred with Representative Marjorie Taylor Greene, Republican of Georgia, who, in the kind of political coincidence that is rarely an accident, found herself at a recent rally in Mr. Crenshaw’s district, declaring, “It is time to embrace the civil war in the G.O.P.”

“I oftentimes argue with someone you might know named Dan Crenshaw,” she later said, his name drawing boos. “I sure do not like people calling themself a conservative when all they really are is a performance artist themself.”

In 2020, Texas was the epicenter of the battle for control of the House, with a dozen suburban seats around Dallas, Houston, Austin and San Antonio all in play.

In 2022, zero Texas Republicans are left defending particularly competitive seats. They were all turned safely, deeply red.

“Not having competitive elections is not good for democracy,” said Representative Lizzie Fletcher, a moderate Democrat whose Houston-area district was also overhauled. To solidify neighboring G.O.P. seats, Republican mapmakers stuffed a surplus of Democratic voters — including from the old Crenshaw seat — into her district, the Texas 7th.

That seat has a long Republican lineage. George H.W. Bush once occupied it. Under the new lines, the district voted like Massachusetts in the presidential election.

For Ms. Fletcher, that means any future challenges are likely to come from the left. The political middle that helped her beat a Republican incumbent in 2018 is, suddenly, less relevant. “There is a huge risk,” she said, “that people will feel like it doesn’t matter whether they show up.”

A proxy fight next door

Phill Cady is showing up. He is one of Mr. Crenshaw’s new constituents, an unvaccinated former airline pilot from Conroe who takes a weekly dose of hydroxychloroquine, the Trump-promoted anti-malaria drug that medical experts have warned against, to fend off Covid.

Mr. Cady was at the Capitol on Jan. 6, 2021, to protest the election results. (He said he didn’t enter the building.) He said Mr. Crenshaw’s acceptance of Mr. Trump’s defeat showed he had “lost his way,” and that Mr. Crenshaw should have helped those facing riot-related charges: “Why hasn’t he fought for the Texans to get out of jail?”

Or, as Milam Langella, one of Mr. Crenshaw’s long-shot primary challengers, described the distance between the incumbent and his constituents: “The district is now blood red and he is not.”

With Mr. Crenshaw facing only scattershot opposition, it was the neighboring open race to replace the retiring Representative Kevin Brady, a business-friendly Republican, that technically drew Ms. Greene to Texas.

On one side is Christian Collins, a former aide to Senator Ted Cruz, who is vowing to join the so-called MAGA wing in the House. He is backed by the political arm of the House Freedom Caucus, the party’s hard-line faction.

On the other side is Morgan Luttrell, a former member of the Navy SEALs who is backed by Mr. Crenshaw and a super PAC aligned with Representative Kevin McCarthy, the House minority leader.

The contest is the first primary of 2022 that the McCarthy-aligned PAC has intervened in, as some McCarthy allies privately worry that the glut of new, deep-red Republican seats could complicate his speakership bid and governance of the House, should Republicans win a majority.

“Does this create incentives to avoid governing? It clearly — clearly, that’s the case,” Mr. Crenshaw said. But he said it is hard to discern the impact of those incentives versus others, like social media amplifying outrage and the increasing sorting of Americans into tribes.

There was tension in how Mr. Crenshaw described who holds the real power in the party, at once dismissing the far right as a fringe nuisance that only seeks to “monetize” division, while also saying traditional power brokers like congressional leaders are no longer the real political establishment either.

“They’re trying to hang on by a thread,” Mr. Crenshaw said of Mr. McCarthy and Mitch McConnell, the Senate minority leader. “They’re trying to wrangle cats.”

The Collins-Luttrell race has become something of a proxy fight over Mr. Crenshaw.

A pro-Collins super PAC used Mr. Crenshaw’s name in an anti-Luttrell billboard along Interstate 45. In a debate, Mr. Collins attacked Mr. Luttrell by saying he had been “endorsed by Dan Crenshaw — I think that name speaks for itself.” At the Collins rally, speaker after speaker called Mr. Crenshaw a R.I.N.O. — a Republican in Name Only.

Mr. Crenshaw dismissed the rally as a “little carnival that came into town” and predicted that Mr. Luttrell would win in a runoff.

But the influence of lopsided districts is not necessarily that the more right-wing candidate always wins. It is that the entire parameters of the debate shift. Notably, neither Mr. Collins nor Mr. Luttrell has accepted that the 2020 election was legitimately decided, one of the issues that first put Mr. Crenshaw in the cross hairs.

Crenshaw’s brand of Republicanism

The walls of Mr. Crenshaw’s campaign headquarters are adorned with unsolicited fan art paying tribute to his patriotism and service, and exemplifying how quickly he broke through into popular culture.

Days before the 2018 election, the comedian Pete Davidson mocked Mr. Crenshaw’s eye patch — comparing him to “a hit man in a porno movie” who “lost his eye in war, or whatever.” Mr. Crenshaw was soon invited onto “Saturday Night Live” to accept an apology. He used the platform to talk about how “the left and right can still agree on some things” and about the value of forgiveness.

“Fighting means persuasion, not just screaming and yelling,” he explained in the interview.

Mr. Crenshaw has an A rating from the National Rifle Association and a 98 percent score from the conservative group Heritage Action this congressional session. Last year, he launched an effort to find whistle-blowers about “woke ideology” in the military. He is flummoxed by being labeled a moderate. “I just — I take a tone that doesn’t turn people off,” he said.

That tone helped him far outpace the top of the ticket in his old swing district and become a rare Republican to carve out a following separate from Mr. Trump’s. But his relationship with the man who has redefined Republicanism is complicated.

In 2020, Mr. Crenshaw was tapped as a keynote speaker at the party’s national convention but made waves for failing to say Mr. Trump’s name. The day of the Jan. 6 riot, Mr. Crenshaw went on Fox News and fumed against those who had “hyped up this day as a day of reckoning” and urged them to “man up and go down there and say enough is enough.” And last August, he told hecklers who attacked him for accepting the result of the election, “You’re kidding yourselves.”

He has not broken fully with Mr. Trump, however. And he opposed impeachment. “I do not think Trump is the devil,” he said last May. “I don’t think he’s Jesus either.”

Still, at Mr. Trump’s Jan. 29 rally outside Houston, when the former president named the House members in attendance, he noticeably omitted Mr. Crenshaw.

He has also not been endorsed by Mr. Trump. “I guess I haven’t asked?” he said.

His critics on the right suggest that in breaking with Mr. Trump, Mr. Crenshaw made the mistake of putting too much stock in his own early popularity. “He was told that he is the future of the Republican Party and that he is going to be around after Trump and he can lead the post-Trump movement,” said Alex Bruesewitz, a Republican strategist who flew in from Florida to rail against Mr. Crenshaw at the Collins rally. Mr. Crenshaw, he said in an interview, “got in over his head.”

Today, in Mr. Crenshaw’s campaign conference room, a doctored painting of a Texas Revolution battle scene shows him as a soldier in buckskins, fighting alongside the Trump sons as the former president on horseback pumps a fist.

“I have a great relationship with him,” Mr. Crenshaw said of Mr. Trump.

Mr. Crenshaw said he did not see false claims of a stolen 2020 election as a “litmus test” in the Republican Party. But his primary against mostly unknown competition is still being watched as a barometer of the base’s discontent for those who break ranks with Mr. Trump.

David Roberts, the co-founder of Texans for True Conservatives, said he expected Mr. Crenshaw to coast to re-election but vowed that 2024 would be different. “We’re going to move heaven and earth,” he said. “He may win this one. But his days are numbered.”

Sitting in his campaign office, in a neighborhood outside his new district, Mr. Crenshaw spoke about the shrinking number of seats that will require Republicans to sharpen their arguments against Democrats — instead of against each other.

“It’s kind of sad, isn’t it?” he said. “I still will, because it’s all I care about. And look, if that doesn’t win out, then the Republican Party is doomed.”