The wind is at Donald Trump’s back, and it’s the kind that doesn’t lessen but build. Last week he won the New York primary with an astounding 60% of the vote to John Kasich’s 25% and Ted Cruz’s 15%. This week he swept the five-state Northeast regional primaries with numbers that neared or surpassed the New York results—54% in Maryland, 57% in Pennsylvania, 58% in Connecticut, 61% in Delaware and 64% in Rhode Island. He beat Mr. Kasich in Greenwich, Conn., the affluent enclave of the old moderate Republicanism. Amazingly, he carried every county in all five states, and every county in New York except Manhattan. With 10 million votes, Mr. Trump is on track to become the biggest primary vote-getter in GOP history. He did well with varied demographic groups, old and young, college graduates, rich and not.

This is the kind of political momentum that tends to grow. A political saying attributed to Haley Barbour is that in politics this is the dynamic: Good gets better and bad gets worse. Very smart analysts and reporters have been translating all these victories into delegate counts, which of course is the key question. But as I look at where we are I think: Get your mind off 1,237; get your mind on the wind at Donald Trump’s back. After all the missteps and embarrassments of the past few months, his support is building.

“I consider myself the presumptive nominee,” Mr. Trump said in his victory remarks. He is.

Nothing wrong with Mr. Cruz and Mr. Kasich continuing to forge on. If you added their votes together the other night, Mr. Trump still would have beaten them. But they’re imagining they still have a shot, and Mr. Cruz just brought in Carly Fiorina as a reinforcement. His admiration of Ronald Reagan is such that he even imitates his blunders. That is what it was for Reagan in 1976 when he picked a running mate before the convention. Desperate gambits are more likely to work when they don’t look desperate.

Here I note an odd aspect of this cycle. Candidates at this point, roughly nine months in, are supposed to be dog-tired, near the end of their personal resources, exhausted and, if they’re not winning, depressed. That’s how it usually goes. But Mr. Kasich is clearly having the time of his life and told me as much in November. Mr. Cruz told me the same thing last week, at a Journal editorial board meeting. I expected to see him tired and dragging. No, fresh as a daisy. Mr. Trump too is clearly having a ball.

I find their joy distressing. America is faced with overwhelming problems, the voters are deeply concerned about our future, and they’re happy little chappies in the cable news town hall. I think they’ve absorbed too well the idea of the power of the happy warrior. I would respect them more if now and then they’d outline our problems and look blue.

In my continuing quest to define aspects of Mr. Trump’s rise, to my own satisfaction, I offer what was said this week in a talk with a small group of political activists, all of whom back him. One was about to begin approaching various powerful and influential Republicans who did not support him, and make the case. I told her I’d been thinking that maybe Mr. Trump’s appeal is simple: What Trump supporters believe, what they perceive as they watch him, is that he is on America’s side.

And that comes as a great relief to them, because they believe that for 16 years Presidents Bush and Obama were largely about ideologies. They seemed not so much on America’s side as on the side of abstract notions about justice and the needs of the world. Mr. Obama’s ideological notions are leftist, and indeed he is a hero of the international left. He is about international climate-change agreements, and leftist views of gender, race and income equality. Mr. Bush’s White House was driven by a different ideology—neoconservatism, democratizing, nation building, defeating evil in the world, privatizing Social Security.

But it was all ideology.

Then Mr. Trump comes and in his statements radiate the idea that he’s not at all interested in ideology, only in making America great again—through border security and tough trade policy, etc. He’s saying he’s on America’s side, period.

And because people are so happy to hear this after 16 years, because it seems right to them, they give him a pass on his lack of experience in elective office and the daily realities of national politics. They accept him even though he is a casino developer and brander who became famous on reality TV.

They forgive it all. Not only because they’re tired of bad policy but because they’re tired of ideology.

You could see this aspect of Trumpism—I’m about America, end of story—in his much-discussed foreign-policy speech this week. I have found pretty much everything said about it to be true. It was long, occasionally awkward-sounding and sometimes contradictory. It was interesting nonetheless. He was trying to blend into a coherent whole what he’s previously said when popping off on the hustings. He was trying to establish that there’s a theme to the pudding. He was also trying to reassure potential supporters that he is actually serious, that he does have a foreign-policy framework as opposed to just a grab bag of emotional impulses.

The speech was an attack on the reigning Washington foreign-policy elite of both parties, which he scored as incompetent and unsuccessful: “Logic was replaced with foolishness and arrogance, and this led to one foreign-policy disaster after another.” Mistakes in Iraq, Egypt, Libya and Syria threw the region “into crisis,” and helped create ISIS. He described democracy-promotion efforts as destructive, costing “thousands of American lives and many trillions of dollars.” Our resources are overextended, our allies must contribute more, our friends don’t trust us, nor do our allies respect us. He called for “a coherent foreign policy based on American interests.” His interest is “focusing on creating stability.” “We must stop importing extremism through senseless immigration policies,” including a “pause for reassessment,” which will help prevent the next San Bernardino.

He positioned himself to Hillary Clinton’s left on foreign policy—she is hawkish, too eager for assertions of U.S. military power, and has bad judgement. This will be the first time in modern history a Republican presidential candidate is to the left of the Democrat, and that will make things interesting. It reminded me of how Mr. Trump, in his insistence that he will not cut or add new limits to entitlement spending, could get to Mrs. Clinton’s left on that key domestic question, too.

He certainly jumbles up the categories. Bobby Knight, introducing him at a rally in Evansville, Ind., on Thursday, said that Mr. Trump is not a Republican or a Democrat. The crowd seemed to like that a lot.

Those conservative writers and thinkers who have for nine months warned the base that Mr. Trump is not a conservative should consider the idea that a large portion of the Republican base no longer sees itself as conservative, at least as that term has been defined the past 15 years by Washington writers and thinkers.