WASHINGTON — Before it became the chief sticking point in a government shutdown drama that threatens to consume his presidency at a critical moment, President Trump’s promise to build a wall on the southwestern border was a memory trick for an undisciplined candidate.
As Mr. Trump began exploring a presidential run in 2014, his political advisers landed on the idea of a border wall as a mnemonic device of sorts, a way to make sure their candidate — who hated reading from a script but loved boasting about himself and his talents as a builder — would remember to talk about getting tough on immigration, which was to be a signature issue in his nascent campaign.
“How do we get him to continue to talk about immigration?” Sam Nunberg, one of Mr. Trump’s early political advisers, recalled telling Roger J. Stone Jr., another adviser. “We’re going to get him to talk about he’s going to build a wall.”
Talk Mr. Trump did, and the line drew rapturous cheers from conservative audiences, thrilling the candidate and soon becoming a staple of campaign speeches. Chants of “Build the wall!” echoed through arenas throughout the country.
Now, Mr. Trump’s fixation with a border wall — the material embodiment of his keep-them-out immigration agenda — has run headlong into the new realities of divided government, pitting him against Democrats who reject the idea out of hand. The impasse is particularly remarkable given that even some immigration hard-liners do not regard the wall as their highest priority and fear that Mr. Trump’s preoccupation with it will prompt him to cut a deal that trades a relatively ineffectual measure for major concessions on immigration.
“I’ve always thought it created a danger that he would trade almost anything in order to get the wall — I think that’s still a potential danger,” said Mark Krikorian, the executive director of the Center for Immigration Studies, a group that argues for less immigration. “I’m still worried about that now.”
That fear has been realized at times when Mr. Trump has explored a deal with Democrats on granting permanent legal status for undocumented immigrants brought to the United States as children, known as Dreamers. The president has always walked away at the last moment from committing to preserving the Deferred Action for Childhood Arrivals program, known as DACA, but on Friday, FAIR, an anti-immigration group, warned him again that it would be a mistake.
To many conservative activists who have pressed for decades for sharp reductions in both illegal and legal immigration — and some of the Republican lawmakers who are allied with them — a physical barrier on the border with Mexico is barely relevant, little more than a footnote to a long list of policy changes they believe are needed to fix a broken system.
The disconnect is at the heart of the dilemma facing Mr. Trump as he labors to find a way out of an impasse that has shuttered large parts of the government and cost 800,000 federal employees their pay. Having spent more than four years — first as a candidate and then as president — whipping his core supporters into a frenzy over the idea of building a border wall, Mr. Trump finds himself in a political box of his own making.