The White House is asking Congress — not Mexico — for $4.1 billion to begin constructing President Donald Trump’s promised massive wall along America’s border with its southern neighbor. But the request threatens to shutter the entire federal government.

The administration wants $2.6 billion for wall-related tasks as part of its budget blueprint for fiscal 2018, and $1.5 billion it could get and spending on the controversial project even sooner via an emergency spending package for the current fiscal year.

But by asking for border wall funding in a Defense Department supplemental request for fiscal 2017, the Trump administration is setting up a major clash with Senate Democrats. That’s because Senate Democrats on Monday warned senior Republicans of a government shutdown standoff if Trump included border wall monies in his fiscal 2017 request, which must pass by April 28 to keep the federal lights on.

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“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, along with Appropriations ranking member Patrick J. Leahy of Vermont, wrote in the letter, which was obtained by Roll Call.

Mick Mulvaney, Trump’s budget director, told reporters Wednesday that the $1.5 billion amount is “all that we think we can spend this year.”

“The next question is going to be: How many miles of wall will that build?” Mulvaney said during a briefing that was embargoed until 12:01 a.m. Thursday.

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“We don’t know the answer to that question because we haven’t settled on construction types, we haven’t settled on where we’re going to start,” the former GOP congressman said. “I think the funding provides for several different … kinds of barriers in different places as we try to find the most cost-efficient, the safest, but also the same border protections.

“The may be different in different areas. So the $1.5 billion gives allows us to start that program,” he said. “And, when we get to the … full budget in May, you’ll start to see some projections out throughout the 10-year window.”

Niels Lesniewski contributed to this report.