Updated at 10:07 a.m. | President Donald Trump will insist Democrats give him a formal “guarantee” for the full amount of federal dollars for his proposed southern border wall, a demand that will further complicate work on a bipartisan immigration bill.

Trump in early September ended the Obama administration’s Deferred Action for Childhood Arrivals (DACA) immigration program, giving Congress six months to pass an immigration bill that addresses those affected by his cancellation plan. Weeks later, the White House released its priorities for that measure, which included full funding for the border wall project.

Congressional aides and policy analysts have acknowledged that Democrats could secure language legalizing the DACA program — or something similar — in that bill, giving Trump an initial tranche of border wall funding — then use Senate rules requiring legislation to clear a 60-vote hurdle to block the remaining amount.

But in an interview late Thursday on Fox News Channel, the president made clear he is mindful that Democrats might give him initial funding, then do their best to prevent him from being able to pay for the rest of the multibillion dollar project.

“That will also be part of DACA or whatever,” he told host Laura Ingraham. “When we get the down payment, we’re gonna have a guarantee, believe me.

“We’re not taking a down payment and then say, ‘Where’s the rest of the money?’” Trump said. “When we take a down payment, I’m going to say, ‘I want to make sure the rest of the money is coming.’”

Trump also said White House projections put the total cost of the project at $18 billion, not more than twice that as some Democrats claim. The president said the cost will be around his estimate because of mountains and rivers along the U.S.-Mexico border that make crossing very difficult. Those areas, he said, will not need a barrier.

He continued to pledge to fulfill what was one of his top campaign promised, saying: “We’re going to have a wall.”