Trump has repeatedly asked for $5.7 billion for the wall, part of which would go toward construction of barriers. The Homeland Security budget is moving to $73.9 billion, down from $93.6 billion requested by President Obama in 2017.
The reductions come after Trump vetoed last week a $36.5-billion bill funding most of the government.
A news release issued by the White House on Thursday said Trump is changing a money-making provision of the Military Construction and Veterans Affairs budget to allow construction of border barriers.
When the White House presents its full budget request on Monday, it will expand on a proposal Trump made to the defense committee in January. Trump will ask for more money to build a border wall than he asked for in his recently passed omnibus spending bill, according to The Associated Press.
The 2019 Pentagon budget of about $700 billion would be used for training and force protection, including for nuclear weapons and operations in Iraq and Afghanistan. According to a draft of the proposed defense budget, Trump wants the Pentagon to have total cash reserves in a non-war contingency fund of $13.6 billion.
At $65 billion, the 2019 budget for the Department of Homeland Security is just under half the amount the agency spent during fiscal 2016. All of the $43 billion being requested is for the nearly 4,000 miles of walls.
DHS Secretary Kirstjen Nielsen on Thursday defended the proposed budget in Washington.
"We need to have borders and if we're not able to secure those borders we can't do our other mission. This legislation not only invests in our border security but ensures funding in areas that support our nuclear deterrent and other high-priority capabilities," she said.