One of President Donald Trump’s main campaign talking points was a very clear promise to build a wall along the southern border of the United States and somehow get Mexico to pay for it.

But over time, the president’s thinking ― or, at least, his rhetoric ― has shifted. This week, as the federal government faces a possible shutdown over Trump’s insistence on more funding for border security, the wall of his campaign trail appears to be nowhere in sight.

Here’s a brief look at Trump’s evolution in talking about that wall:

“Build the wall!”

Trump’s vow that he would “build the wall” was unequivocal throughout his campaign and reiterated in one way or another in almost every rally, speech and interview.

The promise went more or less along the lines of this comment to CNN in July 2015:

“I will build the wall and Mexico’s going to pay for it and they will be happy to pay for it. Because Mexico is making so much money from the United States that that’s going to be peanuts. And all these other characters say, ‘Oh, they won’t pay, they won’t pay.’ They don’t know the first thing about how to negotiate. Trust me, Mexico will pay for it.”

“Certain areas” might include fencing.

In the days following Trump’s presidential win, the wall proposal developed some holes. Former House Speaker Newt Gingrich, who was one of Trump’s earliest and most prominent supporters leading up to the election, admitted shortly afterward that the whole business about Mexico paying for the structure was little more than a “great campaign device.” And Trump told CBS just days after his victory that he would be open to the idea of a fence.

Yeah, it could be. It could be some fencing. President-elect Donald Trump

“Would you accept a fence?” the president-elect was asked by “60 Minutes” correspondent Lesley Stahl.

“For certain areas I would, but certain areas, a wall is more appropriate,” Trump responded. “I’m very good at this. It’s called construction.”

Stahl continued to press him, asking, “So part wall, part fence?”

“Yeah, it could be,” he said. “It could be some fencing.”

Actually, it’s more of a wall-fence combo.

By May 2017, Trump was boasting that his administration was already beginning construction on the wall and that a government funding deal recently reached by Congress included a “down payment on the border wall.” (It didn’t.)

Then-budget director Mick Mulvaney clarified that the administration would be erecting a 20-foot-tall steel fence to replace existing portions of chain-link fencing along the border.

“We’re building it!”

MARK RALSTON via Getty Images Homeland Security Secretary Kirstjen Nielsen looks at a newly renovated section of the 30-foot border fence in the El Centro sector in Calexico, California, on Oct. 26, 2018.

Throughout the first half of 2018, Trump and administration officials were firmly declaring that construction on the wall had begun.

“It’s not ‘build that wall’ anymore. It’s ‘continue building that wall,’” the president said at a July rally in South Carolina. “Because we’re building it!”

What he might have been referring to was what Homeland Security Secretary Kirstjen Nielsen described in April as more like upgrades on the existing barrier along portions of the southern border.

“To us, it’s all new wall,” Nielsen said at a White House briefing. “If there was a wall before that needs to be replaced, it’s being replaced by a new wall. This is Trump’s border wall.”

The truth is that not a single mile of new barrier has been constructed along the Mexican border during Trump’s presidency. As HuffPost’s S.V. Date wrote earlier this month: “There were 654 miles of physical barrier on the day Trump was inaugurated president, and there are 654 miles today.”

When we say “wall,” we may actually mean “steel slats.”

As of December, the president was going with “artistically designed steel slats” to describe his still-promised wall.

Trump addressed the possible government shutdown over border security issues ahead of signing the farm bill on Thursday afternoon. He reiterated some of his main talking points on the need for a border wall, but with his newly phrased caveat.

“At this moment there is a debate over funding border security and the wall ― also called, so that I give them a bit of an out, ‘steel slats,’” the president said. “We don’t use the word ‘wall’ necessarily.”

TRUMP on govt shutdown: "At this moment there is a debate over funding border security and the wall -- also called, so that I give them a little bit of an out, 'steel slats.' We don't use the word 'wall' necessarily, but it has to be something special to do the job." pic.twitter.com/n1uKFFa4UU — Aaron Rupar (@atrupar) December 20, 2018

Maybe we don’t need a wall after all?

Rudy Giuliani, one of Trump’s personal attorneys, also suggested on Thursday that the “wall” could be more of a metaphor for increased border security, which could actually take a number of different forms. He suggested using advanced technology to detect and capture undocumented immigrants instead.

“I don’t see the magic in a wall, as long as there’s some form of improved barrier that picks up penetration,” Giuliani told CNBC. “I could build a wall for him with long-range cameras and security. He needs something. I think he’d compromise if he got most of what he wanted.”