President Trump reviews border-wall prototypes in March in San Diego. (Evan Vucci/AP)

As pressure mounts on President Trump to fulfill his key campaign pledge to build a border wall, he has hit on a quick and easy method to demonstrate progress: Just inflate how much his administration is already spending on the project.

Over the past week, including at a campaign rally Thursday night in Billings, Mont., Trump has begun boasting that he has spent $3.2 billion on the wall at the U.S.-Mexico border — twice as much as has been authorized by Congress.

“We’ve started the wall,” Trump told thousands of supporters at the event. “We’ve spent $3.2 billion on the wall. We’ve got to get the rest of the funding.” Later, he repeated the monetary figure and added: “We’ve done a lot of work on the wall. A lot of people don’t understand that.”

Perhaps that is because it is not entirely true. The Trump administration has begun work on 14 miles of a wall in San Diego and 20 miles in Santa Teresa, N.M., under a $341 million appropriation from Congress last year, according to the Department of Homeland Security.

Additional border security projects, including levee walls and a secondary wall in San Diego, have been planned and could begin soon under $1.6 billion allocated in the spring, the agency said.

But Trump, who touted the $1.6 billion figure in rallies in June and July, has suddenly upped the figure, suggesting at a rally in Charleston, W.Va., in late August that the administration has spent “over $3 billion. It’s moving along very nicely.”

A White House spokesman did not respond to a request for comment. But Trump appears to be adding the money authorized by Congress in the spring with another $1.6 billion proposed by lawmakers in a new spending bill this month.

The White House is demanding more, hoping to win at least $5 billion for the wall in this month’s negotiations. Trump has vacillated in recent weeks on whether he will follow through on threats to force a partial government shutdown at the end of the month if lawmakers do not pony up the funds. The president has said GOP leaders have pressured him not to do so.

During a conversation with reporters Friday on Air Force One, Trump was asked whether he is considering using money from the military’s budget to help pay for the wall.

“We’d rather do it the old-fashioned way,” he said. “We have two options — we have military, we have homeland security. I’d rather get it through politically [in Congress]. If we don’t, I’m looking at that option very seriously.”

In all, estimates for Trump’s wall have ranged between $25 billion and $50 billion. Early this year, Democrats appeared willing to support a figure in the lower edge of that range in exchange for providing a path to citizenship for younger immigrants in the country illegally — a deal that fell apart when Trump insisted on cuts to legal immigration, which Democrats opposed.

The president’s dilemma has become more acute as he approaches November’s midterm elections, which could amount to a referendum on his leadership. His conservative base has grown increasingly impatient over the wall.

Conservative lawmakers and talk-show hosts have publicly supported a shutdown showdown before Election Day. In the spring, 380 sheriffs sent a letter to members of Congress demanding that they fund the border wall.

R.J. Hauman, government relations director for the Federation for American Immigration Reform, a group that supports lower immigration levels, said Trump’s only realistic chance to win significant wall funding is to force a shutdown ahead of the election.

The White House and Congress “have a unique opportunity to fund the way,” Hauman said. “They are sorely mistaken if they think they can wake up the next morning after the election and think it’s okay for them not to deliver.”

Trump sought to reassure his supporters during the Montana rally, while shifting the political blame to Democrats if things do not work out.

“We’re going to get it approved,” he said of the wall funding. “I could do that whole thing in one year, but these guys are holding back. The only thing Democrats are good for is obstruction and resisting. Their whole campaign is resist, resist. I don’t get it.”