The Trump border wall was a key promise Donald Trump made during his presidential campaign.
"We're going to build the wall," he'd tell crowds of supporters, who would chant back that Mexico would pay for it.
How exactly to build the wall is something President-elect Trump will have to figure out.
Former New York City Mayor Rudy Giuliani, a top Trump adviser, said Thursday Trump will keep the promise and build the wall, but he cautioned it would not happen overnight.
"The wall is going to take a while. Obviously he's going to build it. It's a campaign promise. He's not going to break a campaign promise," Giuliani told CNN's Chris Cuomo on "New Day."
Cuomo pointed out there is bipartisan opposition to the idea of a wall in Congress, to which Giuliani said something very interesting that could presage a very interesting debate over executive power.
"Well, he can do it by executive order by just reprogramming money within the, within the immigration service," Giuliani said. "And not only that, they have actually approved a wall for certain portions of the border that hasn't even been built yet. So you could take a year building that out, with what has been approved."
During the campaign, CNN imagined the red tape the wall might encounter in bureaucratic Washington. It'll have to go through government agencies and, theoretically, Congress, which controls the purse strings through bills to authorize programs and then separate bills to appropriate money for them.
Even lawmakers who support a wall might balk at the idea of a major project being started without their say-so.
As CNN's Capitol Hill team reported recently, there is currently little appetite for the wall among top Republicans. Asked three times by CNN if he supports Trump's signature plan to build a wall with Mexico, US Senate Majority Leader Mitch McConnell would only say: "I want to achieve border security the way that's most effective."