He calls it "immoral".
The plan eyes cuts for Social Security Disability Insurance, but Mulvaney argued that was not a core "mainline" part of the retirement savings programme.
They said that unless Trump is able to rally broader support and win more funding for construction in another fiscal year, his plans for a "big lovely wall" that he promised during his election campaign last year may not be realized.
Trump proposes to spend $200 billion to encourage $1 trillion in infrastructure investments largely through public-private partnerships.
The politically perilous cuts to Medicaid, college loans, food stamps and federal employee pension benefits guarantee Trump's budget won't go far in Congress.
The budget lands as Trump's GOP allies in Congress are grappling with repealing and replacing Obama's health care law and looking ahead to a hard rewrite of the loophole-clogged tax code.
Overall, the Trump budget would reduce the deficit from 3.2 percent of gross domestic product in 2017 to 2.2 percent in 2018.
The budget Congress eventually passes may or may not include any of this.
Instead, the Trump tax plan promises an overhaul that would cut tax rates but rely on erasing tax breaks and economic growth to end up as "revenue neutral".
The Senate power broker: "The proposed cuts to important farm and family safety net programs, including crop insurance and the Supplemental Nutrition Assistance Program, are harsh and short sighted". "The question we asked ourselves as we went line by line: Can I ask somebody - a family in Grand Rapids, Michigan - to pay tax money to the government so that I can do "X"?"
House Speaker Paul Ryan of Wisconsin dismissed such criticism as typical rhetoric and praised the budget because it balances over 10 years.
Trump's 2018 budget also would decrease foreign aid spending, slash money going to food stamps and cut billions from welfare.
"We can not continue to measure our compassion or success by the amount of money we spend", said Trump's Office of Management & Budget director Mick Mulvaney in a series of briefings for reporters Monday, a day before the official release of the 2018 budget. "But, as now proposed, this plan falls far too many steps short of the realities working families face, and would leave far too many people behind, including seniors, parents with sick children, and even deployed members of the armed services".
He notes that some Republicans have already distanced themselves from the budget recommendations and that if Republicans actually did seek to enact it, he could "guarantee the American people would rise up and reject their policies and would reject them".
"This is the worst budget for women and women's health in a generation", said Dawn Laguens, the executive vice president of Planned Parenthood Federation of America.
President Donald Trump is proposing to balance the federal budget within a decade by making sharp cuts to social safety-net programs while offering optimistic estimates of economic growth. "We are going to measure compassion and success by the number of people we help get off of those programs to get back in charge of their own lives".
Top GOP leaders in Congress are praising President Donald Trump's budget plan for promising a balanced federal ledger over time.
Over the 10-year budget window, the plan would increase base defense spending by $489 billion and cut nondefense discretionary by $1.6 trillion. "Almost every budget I know of is basically dead on arrival, including President Obama's".
The budget allocates $2.6 billion for improved border security, including $1.6 billion for Trump's physical wall on the Mexican border, though the OMB did not say what percentage of a full wall would be covered by that expense.
Planned Parenthood wouldn't be able to participate in any federal grant programs under Trump's proposed budget.
According to budget tables released by the administration, Trump's plan cuts nearly $3.6 trillion from an array of benefit programs, domestic agencies and war spending over the coming decade - an nearly 8 percent cut - including repealing and replacing Obama's health law, cutting Medicaid, eliminating student loan subsidies, sharply slashing food stamps, and cutting $95 billion in highway formula funding for the states.