The US Department of Homeland Security estimates that constructing fences and walls along the entirety of the US-Mexico border would cost $21.6 billion over three years, according to Reuters.

But US president Donald Trump, who made the wall a centerpiece of his campaign for office, disputed those figures in a series of tweets this morning (Feb. 11).

Trump was referring to recent deals struck with Lockheed Martin and Boeing. Lockheed this week sold 90 fighter jets to the US military for $8.5 billion, which was 8% less than a previous deal. Boeing, which is producing new versions of the planes on which the US president travels, pledged in December to keep the cost under $4 billion. It wasn’t clear in either case how much Trump’s intervention had to do with the price.

In the case of the border wall, estimating the cost has been difficult due to the scale of the project and important variables like how much of it is actually a wall, how tall it is, and so on. Trump has given wide ranging details about the project, at one point promising to build a 55-foot wall, which would be massively expensive, though he has estimated a cost of $12 billion. Whatever the particulars, constructing the wall is expected to be a boon for contractors (paywall, heh).

Trump, who was a real-estate developer for decades, has waxed poetically about the wall’s design. “I want it to be so beautiful because maybe someday they’ll call it the Trump Wall,” he said in 2015. “And do you a beautiful nice precast plank with beautiful everything. Just perfect.”

Reuters reported that Homeland Security secretary John Kelly is expected to receive his department’s report on the wall next week. It details a three-phase project to build 1,250 miles (2,000 km) of barriers along America’s southern border. The US Congress would ultimately have to approve funding for any such project.

It’s worth remembering that more Mexicans are leaving the US these days than entering.