The White House continued to insist on a $5.7 billion price tag to end a partial government shutdown on Sunday, declaring for the first time that the U.S. Army will be the primary contractor building President Trump's border wall.

The latest demand, which House Democrats have declared dead on arrival, came in a letter to key Democratic House committee chairs outlining Customs and Border Protection's readiness to break literal new ground with taxpayer dollars.

'In concert with the U.S. Army Corps of Engineers, CBP has increased its capacity to execute these funds,' said the letter from the White House budget office.

'The Administration's full request would fund construction of a total of approximately 234 miles of new physical barrier and fully fund the top 10 priorities in CBP's Border Security Improvement Plan.'

Trump has argued that a wall between the U.S. and Mexico is needed to block drug cartels and human traffickers from flooding the United States with illegal immigrants and narcotics, and to block unnamed criminals from entering with caravans of Central Americans.

President Donald Trump is sticking to his guns with a demand that Congress give him $5.7 in border wall funding, and revealing that he's already using the Army Corps of Engineers to buil it

A large military presence on the border has already been supplementing Customs and Border Protection agents for months; a letter to Congress on Sunday made 'no mistake' in mentioning the Army Corps, a White House official said Monday, since it would become the biggest contractor if Trump were to declare a national emergency and fund the project without Congress's assent

'[A] physical barrier – wall – creates an enduring capability that helps field personnel stop, slow down and/or contain illegal entries,' according to the letter from Russell Vought, who became the budget office's acting director when Mick Mulvaney became acting chief of staff.

A White House official said Monday morning that the letter's reference to the U.S. Army was 'no mistake.'

'It the president declares a national emergency, the Army Corps of Engineers will kick into high gear,' the official said. 'They're already handing out contracts, and that would speed up a lot.'

The Corps began soliciting bids in mid-2017 for companies to produce 'a mix of border fence, border wall, border patrol roads, border access roads, border lights, border gates (for access to border monuments, for maintenance, and for Border Patrol operational use), border drainage improvements, levee walls, and other miscellaneous improvements, repairs, and alterations.'

Trump told DailyMail.com aboard Air Force One on November 7 that he was considering using military resources to finish construction of his long-promised border wall

One recent contract netted a Galveston, Texas company $145 million to build a levee wall that will shore up parts of the Rio Grande River, and to erect new 18-foot steel-slatted walls atop existing concrete barriers. That construction is slated to begin next month.

Trump has hinted before that he's ready to hand the entire project over to the Pentagon.

DailyMail.com asked him aboard Air Force One in September whether he had a 'Plan B' for his wall if Congress was too stingy with money.

'We have two options,' he said then. 'We have military, we have homeland security.'

He was asked specifically about using the Army Corps of Engineers as a taxpayer-funded construction crew.

Trump said he would prefer to fund the ambitious construction 'the old-fashioned way – get it from Congress – but I have other options if I have to.'

Sunday's letter to key Democratic House committee chairs (page 1) highlighted the U.S. Army Corps of Engineers' involvement in the project to date

The only concession the president made to Democrats on Sunday was an offer to build a 'steel barrier' rather than a concrete wall. Democrats were unimpressed.

The White House said Sunday's letter, as well as details provided during a weekend meeting at the White House, sought to answer Democrats' questions about the funding request. Democrats, though, said the administration still failed to provide a full budget of how it would spend the billions requested for the wall from Congress.

Trump campaigned on a promise that Mexico would pay for the wall, but Mexico has refused.

The letter also included a request for $800 million for 'urgent humanitarian needs,' a reflection of the growing anxiety over migrants traveling to the border – which the White House said Democrats raised in the meetings.

And it repeats some existing funding requests for detention beds and security officers, which have already been panned by Congress and would likely find resistance among House Democrats.

Trump sought to frame a steel barrier as progress, saying Democrats 'don't like concrete, so we'll give them steel.' The president has already suggested his definition of the wall is flexible, but Democrats have made clear they see a wall as immoral and ineffective and prefer other types of border security funded at already agreed upon levels.

House Speaker Nancy Pelosi intends to begin passing individual bills to reopen agencies in the coming days, starting with the Treasury Department to ensure people receive their tax refunds. That effort is designed to squeeze Senate Republicans, some of whom are growing increasingly anxious about the extended shutdown.

White House Senior Adviser Jared Kushner, left, Homeland Security Secretary Kirstjen Nielsen, and Vice President Mike Pence, talked on the steps of the Eisenhower Executive Office Building on the White House complex on Saturday; they hosted a meeting with congressional aides about the partial government shutdown

Among the Republicans expressing concerns was Sen. Susan Collins, R-Maine, who said Senate Majority Leader Mitch McConnell should take up bills from the Democratic-led House.

'Let's get those reopened while the negotiations continue,' Collins said on NBC's 'Meet the Press.'

Adding to concerns, federal workers might miss this week's paychecks. Acting chief of staff Mick Mulvaney said on NBC's 'Meet the Press' that if the shutdown continues into Tuesday, 'then payroll will not go out as originally planned on Friday night.'

Trump reaffirmed that he would consider declaring a national emergency to circumvent Congress and spend money as he saw fit. Such a move would seem certain to draw legal challenges.

Incoming House Armed Services Committee Chairman Adam Smith, D-Wash., said on ABC's 'This Week' that the executive power has been used to build military facilities in Iraq and Afghanistan but would likely be 'wide open' to a court challenge for a border wall. Speaking on CNN's 'State of the Union,' Intelligence Committee Chairman Adam Schiff called the idea a 'nonstarter.'

Trump also asserted that he could relate to the plight of the hundreds of thousands of federal workers who aren't getting paid, though he acknowledged they will have to 'make adjustments' to deal with the shutdown shortfall.