Representative Nita Lowey, D-N.Y., who chairs the House Appropriations Committee, said the request was "not even worth the paper it's written on."
House Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Charles Schumer, D-N.Y., added that Trump caused a government shutdown in December because he defied Congress and demanded a wall. They said lawmakers were prepared to block his demand this time as well.
"The same thing will repeat itself if he tries this again," they said in a joint statement. "We hope he learned his lesson."
The request will come as part of a broader proposal that would call for cutting $2.7 trillion in spending over 10 years for a range of programs, including welfare assistance, environmental protection and foreign aid. At the same time, Trump will seek to dramatically boost the military's budget from $716 billion to $750 billion next year.
The contrast is meant to bring into sharper focus the White House's priorities heading into budget negotiations this summer, even if many lawmakers have already declared the proposals dead on arrival.The wall demands will attract a particular focus, because Trump has shown it to be the one area he will amplify into a political brawl.
He led a government shutdown in December that lasted for 35 days because Congress would not appropriate $5.7 billion to build sections of his long-promised wall. Eventually, Trump relented and reopened the government. A few weeks later, Congress agreed to fund $1.375 billion to finance 55 miles of barrier on the border in Texas.
To try to extract more funds, Trump last month declared a national emergency and said he would redirect more than $6.7 billion from other programs to build even more sections of the wall. The emergency declaration unsettled many lawmakers, including some of his key allies in the Senate. A number of Senate Republicans have said they oppose Trump moving unilaterally to move money without congressional approval and they are expected to pass a disapproval vote in the coming days.
Even with the stiff congressional opposition, Trump's new budget request shows he plans to continue fighting on the issue in the coming months. Congress and the White House must agree on a new budget deal by the end of September. They also must pass a measure to raise the debt ceiling in September or October or they will risk having the government falling behind on its obligations, something that could rattle the economy and financial markets.
By signalling this week that he wants billions of dollars in additional border wall funding to be part of any deal, Trump is sending an early signal to lawmakers of what his demands will be.
The number of people crossing illegally into the United States from Mexico had fallen in recent years, but there has been a sharp increase in recent months. The number of people taken into custody along the border rose 31 per cent last month in large part because of a wave of families trying to enter the United States from Central America.
One senior administration official said the $8.6 billion in additional funding, combined with the money Trump is attempting to redirect with his national emergency declaration, would allow the White House to complete at least 1,160km of barriers - a figure that has long been a White House goal.
White House officials say there are already 196km of barriers that have been completed or are under construction. Some of these barriers are replacing fences that had previously existed, and Democrats have routinely said Trump erroneously claims credit for building walls that don't exist or are far from being completed.
During the 2016 campaign, Trump promised repeatedly to build a wall along the Mexico border. He also said Mexico would pay for it, though the Mexican government has repeatedly refused to finance the project.
Since becoming president, Trump has changed his description of how the wall would be financed, at first saying Mexico would eventually pay the US government back, and later scrapping any mention of Mexico sending money to the United States. Instead, he has insisted the money come from US taxpayers, arguing that criminals, terrorists, and drugs are flooding into the United States from across the southern border.
His top advisers have not provided information to back up many of these assertions, but Kudlow said Sunday that Trump planned to keep fighting.
"He's going to stay with his wall, and he's going to stay with the border security theme," Kudlow said on Fox News Sunday. "I think it's essential."
Pelosi and Schumer said Sunday the money would be better spent on projects like education and workforce development, among other things.
The $8.6 billion request would represent less than 0.5 per cent of the broader White House budget, which will eclipse $4 trillion.The budget request would, among other things, propose cutting $1.1 trillion from Medicaid and other health-care programs over the next decade by turning over more control to states, according to a summary reviewed by The Washington Post.
Medicaid is a health-care program for low-income and disabled Americans, run jointly by states and the federal government. Some Republicans and the White House have repeatedly proposed slashing its benefits, alleging it is wasteful, while many Democrats and a number of Republicans have fought back and sought to expand the program as a way to provide more benefits for the poor.
The White House's new budget plan would also cut another $327 billion from a range of other welfare programs, including those that provide food and housing assistance, in part by imposing mandatory work requirements for certain recipients. It would cut another $207 billion by making changes to student loan programs over 10 years and an additional $200 billion by changing federal retirement programs and making major changes to the US Postal Service.
The budget would call for severe reductions at a number of federal agencies. It will propose a 12 percent cut at the Education Department, a 12 per cent cut at the Department of Health and Human Services, an 11 per cent cut at the Interior Department, a 23 per cent cut at the State Department, a 32 percent cut at the Environmental Protection Agency and a 22 per cent cut at the Transportation Department, according to the summary.
Almost all of the proposals would require congressional approval, and lawmakers have dismissed cuts of similar size in Trump's past budgets. Many Democratic leaders have said they will oppose the sweep of the White House's proposed budget cuts, though White House officials have signalled they plan to fight over the budget much harder this year, believing it provides a sharp contrast between Democrats and Republicans heading into the final year of Trump's first term.
Even with the proposed cuts, the White House proposal would not eliminate the budget deficit until the mid-2030s. This is in part because Trump has instructed aides not to pursue any structural changes to Medicare, the health-care program for millions of older Americans.
