And faced with the fact that he has yet to build an inch of the concrete or steel wall he promised, Trump and his campaign have started relying on a rhetorical sleight of hand: speaking the wall into existence.
"Now, you really mean, 'Finish that wall,' because we've built a lot of it," Trump incorrectly said at a campaign rally last week in El Paso after supporters broke out in chants of "Build that wall!"
As he spoke, giant placards with the words "Finish the Wall" hung from the rafters, an unmistakable signal Trump's aides say reflects the campaign's growing push to convince the President's supporters that the border barrier they imagined him building is already real.
These endeavours underscore the extent to which Trump and his allies are attempting to make 2020 a repeat of 2016 - centered on a portrayal of the nation as under siege from criminal immigrants and other dark forces, and reliant upon a die-hard base of older whites in rural areas.
The strategy comes with serious risks.
It largely assumes that despite Trump's poor poll numbers and his setback in the Midterms, he remains popular enough to rely on the same strategy that delivered him the White House through a thin electoral college victory even as he lost the popular vote by almost three million votes.
"He used immigration pretty effectively in 2018 to motivate voters, but the question is whether it's going to be enough in the states he needs in 2020," said Jennifer Duffy, a nonpartisan election analyst at the Cook Political Report.
"In places like Michigan, Wisconsin, Florida, Pennsylvania and Arizona, can it get the job done?"
Duffy added that if Democrats nominate a strong presidential nominee, Trump might find himself fighting "the last war" as the electorate adjusts to new choices and new debates.
Trump's Republican allies remain confident and said his messaging in recent weeks - however bungled - is nevertheless setting him up for the 2020 presidential election, both in framing the wall as a motivating tool for his core voters and underscoring his commitment to border security.
"You can argue about the details, but strategically, it works," said former Republican House speaker Newt Gingrich, a Trump ally.
"The President wants Beto O'Rourke out there, in contrast, saying that walls kill people and we shouldn't have walls. That could be a snapshot of the 2020 election," Gringrich said of the former Democratic congressman from Texas, a potential presidential contender.
Critics say the President's exaggerated claims about ongoing wall construction will ultimately backfire, undermining his ability to sell himself as a master negotiator who can work his will in Washington.
"The President has always survived by living inside a reality-distortion field,'' said Tim O'Brien, author of TrumpNation: The Art of Being the Donald (2005). "When things don't go his way, he simply creates another narrative."
Trump's claims that the wall is well underway have intensified and become more descriptive in recent weeks as he weathered a record-breaking government shutdown over wall money and bipartisan negotiations to stave off a second lapse in federal funding.
"The wall is very, very on its way," Trump told a conference of law enforcement officials on Thursday. "It's happening as we speak . . . and it's a big wall. It's a strong wall. It's a wall the people aren't going through very easy."
On Saturday, Trump signed a bill that included US$1.375 billion for fencing and other expenditures, a far cry from the US$5.7 billion he previously demanded.
That money can also only go toward building the type of barriers already in use, not the concrete wall Trump highlighted during the campaign and early in his presidency.
By declaring a national emergency, the White House is attempting to bypass Congress and repurpose more than US$6 billion from the Pentagon and other agencies to fund wall construction, but Democrats said they will attempt to stop the move legislatively and in the courts.
"What you're seeing is the mother of all pivots. He's trying to turn [being] outfoxed by Speaker Pelosi into a win by creating a rally cry for the re-elect campaign," said veteran GOP strategist Mike Murphy, a Trump critic.
"For his core base, it'll ameliorate some of the criticism. But it won't help him with general-election voters. He's playing survival politics with his own base and using the illusion of success."
Trump has been building up to this strategy for much of the past year, as conservative angst mounted over the lack of progress on the wall while Republicans had full legislative control. Democrats took back the House in last year's Midterm elections, all but killing Trump's chances of securing adequate funding to build hundreds of kilometres of walls on the border.
The President's original promise, to make Mexico pay for the wall, also remains unfulfilled, succumbing to a political reality that was long obvious despite Trump's claims to the contrary.
The President has complained repeatedly about news coverage depicting the wall as not being built and has told his campaign and communications officials they have to convince people that more of the wall is being built.
He has sought to meet contractors about the wall, even giving specifics on how tall the wall should be.
Trump has repeatedly looked to unorthodox places to get wall money. For example, he has discussed using money meant to help Puerto Rico recover from Hurricane Maria to fund the wall. During a recent presidential trip to the border, Senator John Cornyn, R, told Trump that pulling funds from Puerto Rico could jeopardise financial aid to Florida and Texas, which were also hit hard by natural disasters. Still, the option remains on the table for future expenditures toward the wall, two White House officials said.
While Trump has expressed frustration over Republicans not providing funding for his wall during the first two years of his presidency, GOP congressional leaders have been irritated at times by his shifting demands and lack of attention to the specifics of the legislative debate.
The US$5 billion he demanded earlier this year was an arbitrary number, aides said, after he grew frustrated that Congress only gave him US$1.6 billion - even though his own aides sought that amount.
Trump has often talked about the wall, but current and former White House officials say it has not been a top priority among senior aides. There has been no designated point person on the issue, and Trump's agitation and concern often waxes and wanes.
Several times since taking office, Trump has redefined what he considers a wall. While his Administration funded wall prototypes that were to be built of solid concrete or steel, Congress has placed restrictions into funding bills that only allow for previously deployed fencing designs. Trump has since claimed that such fences, including renovations that replace existing barriers, constitute the wall he promised.
During the last government shutdown, Trump told advisers that Democrats would be more inclined to support the wall if it was called a "steel slat barrier" or some other phrase. But eventually he relented, realising there was no support for the wall no matter what he called it.
Polls show voters blamed the President for the government shutdown, though Trump has since cast it as a strategic win, despite the fact that it did not produce the wall funding he wanted.
According to a person who spoke with the President last Tuesday, Trump has argued that he will eventually be able to claim that he "shut down the government over this wall" and that his supporters will approve.
Some of the President's allies have said that politically, Trump's "finish the wall" rhetoric should be interpreted more metaphorically than literally.
"The point of the wall is to show how the President is committed to border security and painting Democrats into a corner as being against that," said former White House legislative director Marc Short.
"Finish the wall,'' he said, "is a good message as long as the wall is a metaphor for border security."
A White House official said it is even broader than that.
"Finish the wall is really: 'Finish what we started.' It's about the Trump presidency, more than anything," said the official. "It's telling the voters to stick with us, finish what we started, as the Democrats pursue the Green New Deal or Medicare-for-all."
Veteran Democrats acknowledge the power of Trump's pitch in a deeply divided nation, but question whether it can work again in 2020 in the same way it worked with some swing voters in 2016.
"It's an applause line that has emotional resonance - and it's completely irrational," said Senator Richard Blumenthal, D. "There is, I think, a broad majority of Americans who are really fed up with the false contention that the wall is somehow the equivalent to border security. It's a vanity project for the President."
Many moderate Republicans, such as Representative Brian Fitzpatrick of Pennsylvania, a former FBI agent who represents the Philadelphia suburbs, have noticed Trump's evolving updates on the wall - and have grown frustrated with his insistence on calling for a wall.
"I never even use the term wall," Fitzpatrick said. "That conjures up images of a brick-and-mortar structure, from sea to shining sea, when it's far more complicated."
Democrats have pledged to file legal challenges to Trump's declaration of a national emergency, setting up a constitutional clash over the President's attempt to usurp spending power from Congress.
A court battle could stretch out for months or years, but Trump is already determined to tell his supporters he is moving full speed ahead on building the border wall.
"He fashions his own reality," said Barbara Perry, a presidential historian at the University of Virginia's Miller Centre of Public Affairs.
"It's like John Kennedy going out after the Bay of Pigs and saying, 'What a great victory.' But for [Trump's] base, I'm just not sure that it matters to them."
