Sam Nunberg, a political advisor on President Donald Trump’s 2016 presidential campaign, told the New York Times that the concept of building a wall on the southern border of the US started as a way to get Trump to talk about immigration.

Trump biographer Michael D’Antonio told The Times the idea of building a wall catered to Trump’s love of building and branding things: “I think he hears the beep, beep, beep of a cement truck backing up and the product being poured and the wall rising … He can grasp that stuff. He loves it.”

Times Acting Chief of Staff Mick Mulvaney said on “ Meet the Press ” Sunday that details on the makeup of the wall were not discussed at Saturday’s meeting with Vice President Mike Pence and Democratic Congressional leaders.

A former political advisor to President Donald Trump said the idea of building a wall along US-Mexico border was created out of a need to get Trump to talk about immigration.

Sam Nunberg told the New York Times getting Trump to talk about building a wall was the easiest way to get him to discuss immigration on the campaign trail.

Nunberg who advised Trump during his 2016 presidential campaign and was later subpoenaed by special counsel Robert Mueller as part of his investigation of the Russia probe, cited a conversation with fellow advisor Roger J. Stone Jr.

“How do we get him to continue to talk about immigration?” Nunberg said. “We’re going to get him to talk about [sic] he’s going to build a wall.”

Michael D’Antonio, an author and journalist who wrote a biography on Trump in 2015, told the The Times building a wall caters to the core of Trump’s personality.

“I think he hears the beep, beep, beep of a cement truck backing up and the product being poured and the wall rising,” D’Antonio said. “He can grasp that stuff. He loves it.”

Read more: Trump and Pence offered completely different accounts of a meeting to resolve the government shutdown

What was meant to serve initially as a way to encourage Trump to talk about immigration now sits at the center of the current partial government shutdown. All the while, the rhetoric around how or what exactly will be built has continued to change.

Outgoing White House chief of staff John Kelly said the addition to the southern US border wouldn’t even actually be a wall.

Acting Chief of Staff Mick Mulvaney, who appeared on “Meet the Press” Sunday morning, said despite being a mandate of the group, details on the makeup of the wall were not discussed Saturday at a meeting led by Vice President Mike Pence and other top members of Trump administration with Democratic Congressional leaders.

“Do you think that ports of entry need to be included? Do we think that? Yes, ok let’s put that in the thing we agree on. Do we disagree on a wall, or do you really agree that maybe a steel fence qualifies as a fence and not a wall, and we want to build a steel barrier anyway,” Mulvaney told Chuck Todd. “Having those types of definitional conversations. We never even got to that.”

Instead, Mulvaney said Democrats brought up technical requests, something he said they had not previously asked for.

“So I think this is going to drag on a lot longer,” Mulvaney said. “I think that is by intention.”