Mr. Trump’s vision for the White House, and arguably a major part of his appeal, is that he’ll bring this successful business model to Washington, apply it both to Congress and world-wide, and triumph over the status quo. He seems to view most of human life as a series of transactions and in the unsentimental, Darwinian universe he inhabits, the deals are always zero-sum.

Take the Keystone XL pipeline. He’d “100%” provide the approval the Obama administration has denied, “but I would rather negotiate a better deal.” Mr. Trump observes that “without eminent domain, that pipe wouldn’t go 15 feet,” so he would ask its developers to “give the people of the United States a piece of the profit.” He throws out 25%. If they refuse, “then I’d say let’s not do it. And you know what’s gonna happen? They’re gonna come back and give it to me. So we’ll take 15% then, OK.”

Mr. Trump discusses policy at such a high altitude that details about how his vision will be realized are often thin to nonexistent. He waves off concerns that his tax reform—which he says he wrote himself with one economist and one tax expert, “who are respected”—would blow up the federal fisc. The plan would collapse the seven individual income brackets down to four, with a top rate of 25%, and slash the corporate rate to 15%, adding about $10 trillion to the deficit on a dynamic basis. Normal voters don’t care about white papers, he observes.

Only journalists, Mr. Trump says, expect “a 14-point thing on something, on anything, right, you know, policy. . . . I always find the people don’t want it.”