You almost have to admire Defense Secretary Pete Hegseth taking the stage at the Ronald Reagan presidential library and immediately opening fire. “Most who invoke Ronald Reagan’s name today, especially self-styled Republican hawks, are not much like Ronald Reagan,” he said. “Donald Trump is the true and rightful heir of Ronald Reagan.” Who says the Gipper is irrelevant in Republican politics?

Mr. Hegseth aimed to locate the Trump project in Reagan’s mantra of peace through strength, and their slogans are the same. But the history of Reagan’s success is worth recalling as Mr. Hegseth accuses others of besmirching the 40th President’s legacy. Reagan rebuilt the U.S. military but also took political risk to negotiate with communists to win the Cold War, and Mr. Hegseth says President Trump is rerunning that playbook.

That doesn’t get the Reagan history right. Reagan negotiated from strength because he first built up that strength, both military and economic. He deployed midrange nuclear missiles in Europe despite ferocious Soviet opposition. The Soviets tried to break the U.S. alliance with Europe, and they only turned to serious negotiating when they concluded they couldn’t compete with the U.S.

Today the U.S. faces two nuclear peer adversaries, China and Russia, both global and ideologically hostile powers like the Soviet Union. And they are working together. Mr. Trump is so far making concessions to both and is spending less on defense as a share of the economy than Jimmy Carter did in 1979.

Mr. Hegseth said the defense budget is going up. “My kids and yours will someday talk about the Trump buildup,” he said. We’re ready to help the President make the case, and his one-time cash infusion in this year’s Republican budget bill was a start. But now what? Mr. Trump’s fiscal 2026 budget proposed a defense cut after inflation.

The defense secretary is right that Reagan hesitated to use military force abroad. But then Mr. Hegseth revived Reagan Defense Secretary Cap Weinberger’s test for U.S. intervention abroad. That doctrine prescribes force only as a last resort for a vital interest, and only if it’s popular, among other requirements. “This is sound stuff,” Mr. Hegseth said.

But Reagan and his Administration never fully accepted those tenets. Bill Safire, the conservative columnist, described the doctrine in the New York Times at the time as “only the fun wars” and a vow not to defend ourselves until the stakes are dire. As Safire put it: “Our tradition has been to accept risks for a just cause.”

That point matters because you can’t reduce Reaganism to “out with utopian idealism, in with hard-nosed realism,” as Mr. Hegseth averred. The Reagan grand strategy blended idealism with realism–naming an evil empire, while arming even unpalatable enemies of communism across the world.

The Chinese Communists may not be fomenting revolution abroad the way the Soviets did–for now–but their ambitions are still to become the pre-eminent global power, and Vladimir Putin is their junior partner. Mr. Trump casually said recently that Ukraine is losing its war, but Reagan would understand that Ukraine’s defeat would be a loss for the West that makes the U.S. less secure.

Mr. Trump has made several policy choices worthy of Reagan, notably his Golden Dome homeland missile shield and enforcing his word that Iran can’t have a nuclear weapon. Both Presidents evince a genuine hatred of nuclear weapons and the awful human cost of war. President Trump carries an instinct for U.S. primacy in the world, albeit without Reagan’s decades of arguments about freedom and the virtues of free societies.

America’s enemies are doubtless pleased that Mr. Hegseth is so focused on settling scores about the Iraq War and firing inside the GOP tent. But if there’s a silver lining to his historical rewrite, it’s that the Trump team understands that Reagan’s legacy is important to embrace. Some in the MAGA coalition have dismissed this as “Zombie Reaganism” and claim that the U.S. would be better off if Pat Buchanan’s isolationism had prevailed.

Don’t believe it. The Administration is associating with Reagan because Republican voters still see themselves in his tradition and coalition. Mr. Trump knows who is the standard bearer for Republican electoral and strategic success. We wish his policies were as similar to Reagan’s as his slogan.

— Wall Street Journal