"I don't care what the political ramifications are, our immigration laws and border security have been a complete and total disaster for decades, and there is no way that the Democrats will allow it to be fixed without a Government Shutdown", Trump said in a tweet Tuesday afternoon.
In the past, Trump has requested as much as $25 billion for the wall.
Trump campaigned on the promise of building a border wall to deter illegal immigration and making Mexico pay for it. Mexico has refused.
He said that needed border security reforms included the wall, the visa lottery, catch-and-release policies, and immigration laws.
Trump wants Congress to pass legislation that addresses immigration issues.
'I would have no problem doing a shut down.
President Donald Trump walks with his granddaughter Arabella after returning to the White House from a weekend in Bedminister, New Jersey.
The AP reported last month that children held at an immigration detention facility in Roanoke, Virginia, said they were beaten while handcuffed, locked in solitary confinement and left nude and cold in concrete cells.
Trump has come under intense criticism for his zero-tolerance immigration policy, which prioritises prosecutions of people who enter the USA illegally.
"Border Security is National Security, and National Security is the long-term viability of our Country", he added.
Trump returned to the idea after a meeting at the White House last week with House Speaker Paul Ryan, R-Wis., and Senate Majority Leader Mitch McConnell, R-Ky., where they were said to have agreed on the way forward on government funding for the budget year that starts October 1. "You know, I think we're going to make sure we keep the government open, but we're going to get better policies on immigration".
And on Iran, Mr. Trump said that he would be willing to meet with Iran's President Hassan Rouhani in light of other "great" meetings with known adversaries including Russian President Vladimir Putin and North Korean dictator Kim Jong Un.
"I just wish Trump would realize, that of all secret weapons of our secret weapons of Donald Trump, if he'd build the wall, the media will go insane, it will distract over everything, and his poll numbers will go through the roof", she said.
Numerous children have been accused by immigration officials of belonging to MS-13 and other violent gangs, an activity Trump has used to justify his "zero tolerance" policy of prosecuting immigrants caught entering the country without permission.
Meanwhile, Ryan and McConnell, facing the November midterm election that could result in changes of power in the House and Senate, are leery about a government shutdown that could prove unpopular in the weeks ahead.
"I would be certainly willing to close it down to get it done", he said.
Senate Majority Leader Mitch McConnell (R., Ky.) downplayed the potential for a government shutdown, which would take place October 1, the end of the fiscal year and just weeks before the midterm elections.
Current funding for the government expires September 30. McConnell canceled most of his chamber's recess to give senators time to work on the annual spending bills. Each time congressional leaders have reached a broad bipartisan agreement on spending, he has expressed anger that it does not include money for the wall and threatened to torpedo the deal.
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The $5 billion is well above the $1.6 billion in the Senate version of a bill funding the Department of Homeland Security. The higher amount matches what Trump has privately sought in conversations with Republican lawmakers.
"We have laws that don't work", Trump said, praising ICE and border security agents for enforcing the law against criminal illegals.