The ‘presumptive nominee’?

Those folks in the Republican establishment who rigged the primary process against Donald Trump sure did a miserable job.

The Donald on Tuesday rampaged through the northeast, hammering Ted Cruz and John Kasich in Maryland, Pennsylvania, Delaware, Connecticut and Rhode Island, winning each by at least 30 points. He now has 950 delegates, within sight of the magic number of 1,237.

Not surprisingly, the bombastic Mr. Trump couldn’t restrain himself. “I consider myself the presumptive nominee,” he said Tuesday night. He went on to say that Hillary Clinton will “be easy to beat” and that she wouldn’t get 5 percent of the vote if she “were a man.”

Well, that settles it then.

The breadth of Mr. Trump’s rout was significant. He won a majority of men, women, evangelicals, lower-income voters and voters with college degrees. He didn’t lose a single county, anywhere.

With 10 states left, the math leans in Mr. Trump’s favor.

“He’s a safe bet in New Jersey and West Virginia,” writes Nate Cohn of The New York Times. “He could win a further 40 delegates” in Washington, Oregon and New Mexico, but remains “an underdog in winner-take-all states in the West and plains: Montana, South Dakota and Nebraska.”

That leaves two big prizes: California and Indiana, featuring 229 pledged delegates. With Mr. Trump polling well in the Golden State, the Cruz-Kasich alliance in next Tuesday’s Indiana primary is perhaps the last chance disgruntled Republicans have of wresting the nomination away from him. A win for Mr. Trump in the Hoosier State solidifies him as a heavy favorite to take the GOP prize on the first ballot.

If Mr. Trump secures the necessary delegates heading into the July convention, any back-room ploys risk playing into Mr. Trump’s narrative while fostering further distrust among an already cynical electorate. Some Republicans have floated the idea of launching a third-party alternative, but it’s hard to imagine what that would accomplish other than to further gild Hillary Clinton’s road to the White House, much as Ross Perot did for her husband.

Mr. Trump remains a polarizing figure with sky-high negatives who offers only vague policy positions on a wide range of issues. Ironically, as the nominee he will need the very GOP establishment that he regularly disparages if — his boasts notwithstanding — he hopes to avoid a November rout. Mr. Trump simply can’t afford to have a large number of traditional Republican voters stay at home because they want no part of him.

As it becomes more and more likely he will prevail, expanding his reach beyond the rebellious, disgruntled and disaffected becomes Mr. Trump’s greatest challenge.