I’ve noted before that Donald Trump lives by a famous dictum from Joseph Goebbels, the Nazi propagandist: “When one lies, one should lie big, and stick to it.” (Goebbels attributed this tactic to the English.) And the President has outdone himself with his Administration’s new budget proposal for the 2020 fiscal year, which is entitled “A Budget for a Better America: Promises Kept. Taxpayers First.”

“Promises kept” has a particularly nice ring to it. Almost as nice as what Trump said on that fateful day, June 16, 2015, when he descended the escalator at Trump Tower. “Save Medicare, Medicaid, and Social Security without cuts,” he declared. “Have to do it.” Throughout the Republican primary campaign, Trump repeated this pledge many times and also accused his G.O.P. opponents of wanting to slash the three big entitlement programs. In the general-election campaign, he stuck to the same mantra. A few days before Election Day, he suggested that Hillary Clinton wanted to “destroy” Medicare, the public health-care system for the elderly, which she had vowed to expand, and claimed that he alone would “protect” it.

So how does the “Budget for a Better America” treat Medicare and the other programs that Trump vowed to safeguard at all costs? By calling for even larger cuts to them than the White House proposed this time last year, when it formally abandoned Trump’s campaign pledges. The budget for the 2019 fiscal year called for five hundred and fifty billion dollars in cuts to Medicare over ten years. With the budget deficit skyrocketing as a consequence of the Trump-G.O.P. tax bill, the 2020 budget would reduce spending on Medicare by eight hundred and forty-five billion dollars over the next decade. Even in Washington, that’s a lot of money.

The cuts to Medicare would be imposed as the budget allots billions of dollars a year in extra spending to the Pentagon and another $8.6 billion for Trump’s wall along the southern border. The economies would be achieved largely by reducing payments to doctors, hospitals, and other health-care providers, which could affect benefits and drive some providers to leave the program. Rather than spelling this out, the document adopts the language of Newspeak: “The Budget proposes to reduce wasteful spending and incentivize efficiency and quality of healthcare in Medicare, extending the solvency of the program for America’s seniors consistent with the President’s promise to protect Medicare.”

The budget treats Medicaid, the federal health program for poor people and children, in even more draconian fashion. Reflecting a long-standing priority of the Republican Party, the budget would convert Medicaid into a decentralized system administered by the states and financed by federal block grants. By indexing these grants to the rate of consumer-price inflation, which rises more slowly than inflation in the health-care sector, the budget would substantially reduce the federal spending commitment going forward. In addition, it would eliminate funding that the Affordable Care Act provided for individual states to expand Medicaid to more recipients—funding that more than thirty states have taken advantage of in recent years.

Even for an ardently conservative Administration like this one, you might think that would be enough cuts to health-care spending. No. The budget also proposes to eliminate some federal subsidies that the A.C.A. provided for the purchase of private insurance plans by people who aren’t quite poor enough to qualify for Medicaid. “The budget overall would cut funding for Medicaid and ACA subsidies by $777 billion over ten years, compared to current law,” Hannah Katch, an analyst at the Center on Budget and Policy Priorities, a liberal think tank, noted.

It is true that, these days, White House budgets often don’t amount to much. Effectively, they are extended wish lists, which the spending authorities on Capitol Hill often set aside, especially when the government is divided, as it is now. But even a White House wish list is a significant document, because it expresses the spending priorities of the Administration and the President. In this instance, those priorities run directly counter to the message that Trump conveyed on the campaign trail.

No surprise there, you might say. It’s been clear from the beginning that Trump was selling snake oil and that his pledge to protect the safety net was about as valuable as a certificate from Trump University. But it is instructive, nonetheless, to see his mendacity expressed in cold numbers, and it also raises an interesting political question.

What will Trump do when the 2020 campaign heats up and the Democratic candidates hurl back at him the details of his spending proposals? On Monday, some Democrats were already doing this. Bernie Sanders tweeted, “This budget does the exact opposite of what Trump promised the American people.” Kamala Harris tweeted, “This would hurt our seniors and is yet another piece of evidence for why we need a new president.”

My guess is that Trump might well end up disowning his own handiwork. Budgets? I had nothing to with them. I was too busy building the wall and hanging out with Little Rocket Man. Hopefully, the Democrats (and the voters) won’t let him get away with it.