The White House has made its first request for money to build the wall. It asked Congress, not Mexico.

President Donald Trump’s administration submitted a supplemental budget request to Congress Thursday, requesting $3 billion to be tacked on to the Department of Homeland Security appropriation bill for Trump’s proposed border wall and implementation of executive orders — expected to be used for hiring border and ICE agents and expanding of detention and deportation funding. This would be only a fraction of the border wall’s estimated cost. The 2018 budget proposal has an additional $2.6 billion for wall construction. Office of Management and Budget Director Mick Mulvaney said the president would request a total of $4.1 billion between fiscal years 2017 and 2018 for the wall.

The 2017 supplemental budget request also proposes a $25 billion defense budget increase and an $18 billion budget cut to nondefense programs.

Trump keeps saying the wall is “ahead of schedule” but it’s still unclear what that schedule is or what the wall will even look like. The White House, which is still looking at proposals from government contractors, seems to be buying time — asking for some funding first while it decides how to build.

That strategy — fund now, figure out the rest later — has raised some eyebrows across party lines in Congress. Democrats have threatened to take the government to the brink of a partial shutdown, if necessary, to block wall funding. With no detailed plan from the White House, some Republicans aren’t a sure bet for support either.

Democrats have some leverage with appropriations bills

Democrats may not have control of the House or the Senate, but when it comes to appropriating funds for the wall, they have leverage. Congress needs to pass the appropriations bills by April 28 to keep the government open. Democrats can block the Department of Homeland Security funding in a filibuster. Any delay that lasts beyond April 28 will lead to a shutdown of the department.

On Wednesday, one senior GOP congressional aide told Politico a shutdown fight “looks like it probably is going to happen."

Minority Leader Sen. Chuck Schumer (D-NY) and fellow Senate leaders told Republicans that any attempt to pass funding for the border wall in the 2017 appropriations bill would be met with unified Democratic resistance.

“We believe it would be inappropriate to insist on the inclusion of such funding in a must-pass appropriations bill that is needed for the Republican majority in control of the Congress to avert a government shutdown so early in President Trump’s Administration,” the Senate Democratic leadership team wrote in a letter addressed to Senate Majority Leader Mitch McConnell on March 13.

Unlike the American Health Care Act and President Trump’s Cabinet confirmations, which only needed a simple majority of 51 votes, Republican senators will need 60 votes to end debate on the appropriations bill and get it passed — which means they need to get their party in line and win eight Democrats to their side.

Members of both parties are skeptical of funding the wall

Appropriation fights come to the brink of government shutdown often; it happened as recently as December 2016, when Democrats threatened to initiate a shutdown if Republicans didn’t pass the Miners Protection Act, which would have guarded former miners’ health care and benefits. It was just a threat — the Democrats didn’t have any intention of causing an actual shutdown.

That doesn’t make the funding for the wall safe. There are some hints from Capitol Hill that Democrats might not be alone in this stand against the wall.

So far, every cost estimate of the construction has shown the wall will be expensive and difficult to build — between $13 billion and $21 billion. A specific price tag and building plan have yet to be announced, and the White House is still requesting proposals.

"I prefer to see a plan first before we start appropriating money,” Sen. John Cornyn (R-TX) told Politico. "We won't just appropriate money and have the plan TBD. And I've got some questions.”

One of those questions for Republicans is where the money will be coming from.

“I generally don’t vote for anything that’s not offset,” Sen. Jim Risch (R-ID) told Fox News in January. “Everything needs an offset.” In other words, increasing spending on the wall will require cuts somewhere else.

Republican House Speaker Paul Ryan, who once led the budget hawks in the House Budget Committee, has framed this as a “national security issue,” in order to reconcile his fiscal conservatism and the president’s wishes. He has been adamant that the Republican Party will stay unified on the issue.

“[The wall] is something we want to get on right away,” Ryan said at a Politico Playbook event in January. “It’s a promise we are going to help [Trump] keep.”