Spending cuts alone do not a fiscal conservative make. Remember that as President Trump claims to be one, bigly, based on the deep cuts he’s proposed in just about everything the government does other than defending the nation and distributing Social Security and Medicare checks.

Instead, partly because of those cuts, Mr. Trump is forfeiting the mantle of fiscal conservatism that the Republican Party claimed for a century. This is no break with his party, however: Mr. Trump is completing a fiscal trend that reaches back at least two decades to Newt Gingrich’s revolution, when Republicans broke Democrats’ near lock on congressional majorities, and through the George W. Bush years, when Republicans last controlled both the White House and Congress. A whole generation of Americans has come of age since most Republicans abided by true fiscal conservatism — that is, prizing small government and low taxes but being willing to raise taxes to keep a healthy balance sheet.

Trumpism would just take fiscal irresponsibility to a new level. Like “Ryan Republicans” — defined for nearly a decade by the budget plans of Representative Paul D. Ryan, now House speaker — Mr. Trump is promising multitrillion-dollar tax cuts that overwhelmingly benefit the top 1 percent. Unlike Ryan Republicans, Mr. Trump says there will be no compensating reductions in Social Security and Medicare, the entitlement programs that are — along with insufficient revenues — driving projections of unsustainable federal debt as the population ages and claims benefits. (The president used to say Medicaid was off-limits, too, until the Republican health care proposal took aim at the program for the poor and disabled.)

What Mr. Trump proposes to cut is the relatively small 15 percent share of total federal spending that nonetheless covers most government operations, other than the Pentagon and entitlement programs. That so-called nondefense discretionary spending includes a raft of programs that disproportionately benefit “the very people that President Trump said would be his priority, people who have been left behind by today’s economy or live in distressed urban or rural communities,” said Robert Greenstein, president of the liberal Center on Budget and Policy Priorities. Among them: opioid-addiction treatments and training for workers whose jobs were lost to offshoring.