President Donald Trump will slice into nondefense spending to pay for a 10 percent increase in defense spending in his fiscal 2018 budget, a senior Office of Management and Budget official said Monday. In addition, officials said the so-called skinny budget, or budget outline, will be shipped to Congress on March 16.

Trump is proposing a $54 billion increase in defense, taking defense up to $603 billion in fiscal 2018. Nondefense accounts would be cut by a corresponding $54 billion, in part by cuts in foreign aid.

The White House was set to deliver draft topline budget numbers to departments and agencies on Monday in a process called “passback.” During passback, OMB officials notify departments and agencies of their approved budgetary levels, which may differ from the agencies’ budget requests. The passback decisions can also include policy changes. Agencies can appeal the decisions to the OMB.

The Pentagon will make recommendations for where to allocate its additional $54 billion, and all non-security agencies will take a hit, a person briefed on the Trump plan told CQ Roll Call.

The plan would break the current firewall between defense and nondefense as specified in the 2011 deficit reduction law, which lowered the caps on defense and nondefense spending after a special congressional committee was unable to agree on $1.2 trillion in additional deficit reduction.

Under that law, fiscal 2018 defense spending is limited to $549 billion and nondefense spending to $515.4 billion.

Raising defense to $603 billion instead would restore military spending to the earlier, pre-sequester limit in the 2011 law. But by cutting nondefense by the same amount, the budget would shrink domestic spending even below current levels.

Democrats immediately vowed to resist such cuts.

“This budget proposal is a reflection of exactly who this president is and what today’s Republican Party believes in: helping the wealthy and special interests while putting further burdens on the middle class and those struggling to get there,” Senate Minority Leader Charles E. Schumer said in a statement.

OMB Director Mick Mulvaney confirmed the topline budget numbers during the White House’s daily press briefing, saying that the skinny budget would propose rebuilding the military, restoring nuclear capabilities, increasing school choice and securing the U.S. border.

“This is not a full-blown budget,” he said. “That will not come until May, so you’re not going to see anything in here that has to do with mandatory spending, entitlement reforms, tax policies, revenue projections or the infrastructure plan. This blueprint was never going to be that, as I made clear during my Senate confirmation. It is a topline number only.”

Mulvaney said the budget outline will not add to the “currently projected [fiscal] 2018 deficit.” He did not detail the domestic programs that will be cut under the proposal, but said: “It reduces the money that we give to other nations. It reduces duplicative programs. And it eliminates programs that simply do not work.”

He did say programs to be reduced are all programs Trump has talked about publicly.

With respect to foreign aid cuts, which do not make up a substantial part of the annual budget, Mulvaney said it’s consistent with what Trump has said.

“Yes. It’s a fairly small part of the discretionary budget, but it’s still consistent with what the president has said. When you see these reductions, you’ll be able to tie it back to a speech the president gave or something the president has said previously,” Mulvaney said. “We are taking his words and turning them into policies and dollars.”

The larger budget request, Mulvaney said, would be sent to Congress in the first part of May.

White House Press Secretary Sean Spicer was asked numerous questions about what the fiscal 2018 budget would look like and how the administration would reach the 60 votes needed in the Senate to change current budget law, thereby allowing the requested increase in defense spending.

Spicer appeared confident the White House would be able to sway some Democrats to support their proposal — despite Democrats saying for years that any increase to defense spending must be accompanied by an equal increase in nondefense spending.

“I think that when it comes to our nation’s security, specifically our nation’s military, I don’t think it’s a partisan issue,” Spicer said.

Trump laid out his budget priorities to the nation’s governors Monday morning, confirming that his coming fiscal 2018 budget will propose a big defense spending increase and slash spending in other areas.

Trump told the governors that his first budget will be a spending plan of “great rationality.” The budget plan will also focus heavily on “economic development and things such as that,” he said, promising to go into “great detail tomorrow night” when he addresses a joint session of Congress.

Jennifer Shutt contributed to this report.