Donald Trump’s landslide victory in the New York GOP primary was a game-changer. It ended his Wisconsin slump and set the stage for an across-the-board sweep next Tuesday in Pennsylvania, Maryland, Delaware, Connecticut, and Rhode Island.

Mr. Trump’s vote count exceeded his pre-primary polling average by nearly 10 percentage points. Perhaps most important, the win gave him 89 more delegates for the RNC July convention.

So Mr. Trump is now the prohibitive favorite to win the GOP nomination — although there is still much dispute about this. I believe, even if he comes up short of a majority 1,237 delegates, he will still get a first-ballot victory. There will be roughly 190 uncommitted delegates at the Cleveland convention. And Mr. Trump, with his art of the deal, can be persuasive.

What hasn’t received enough attention following New York is how Mr. Trump did it, and how it will enhance his position in the rest of the primaries. My theory is this: Mr. Trump cleverly turned the tables against Ted Cruz in regard to the nationwide delegate fight, especially in Colorado. Mr. Trump outflanked Cruz.

By calling the delegate-selection process “rigged” and arguing that Colorado had an election without voters, Mr. Trump turned a loss into a victory. Why? Because he put Mr. Cruz in the unenviable position of defending the status quo delegate-selection process.

Now, Mr. Cruz played by the rules in Colorado and elsewhere. And Mr. Trump was caught flat-footed, and to some extent had to be embarrassed by his own weak delegate-gathering team.

However — and this is the key point — Mr. Cruz argued time and again that the rules were the rules and that he simply played by them. And as Mr. Trump continuously attacked the RNC rules as being undemocratic, disenfranchising to voters, and creatures of out-of-touch Republican-party regulars, he put Mr. Cruz in the position of backing the establishment. Just where Mr. Cruz doesn’t want to be.

Moreover, in attacking the delegate process, Mr. Trump was able to restore and even enhance his position as the anti-establishment outsider. The agent of change. That’s precisely what GOP voters favor.

Now, Colorado was a deleterious delegate story to begin with. A planned direct primary vote was cancelled. A friend relates the disturbing story of his moderate Republican brother who owns a small railroad and who caucused for Mr. Trump. Mr. Trump won that local caucus by 60%. But as the process moved up to the county level, then the congressional district level, and finally the state level, Mr. Trump got zero delegates.

At a minimum, this process was whacky, convoluted, and opaque. At its worst, it was rigged against GOP voters.

Other states have produced similar horror stories. Pennsylvania may be positioned to deliver the most ridiculous. Whoever wins the direct Pennsylvania primary next Tuesday gets only 17 out of 71 delegates. So no matter who wins, 50-something delegates will still be uncommitted. That’s crazy.

Actually, I think the whole GOP selection process is crazy. Why not a simple, direct, winner-take-all primary election? The person with the most votes gets all the delegates. Nice and simple.

RNC chair Reince Priebus might want to think about this progressive democratic reform. After 100 years or so, it’s time for a change. But back to the Trump New York win. Mr. Trump trashed the current delegate system while Mr. Cruz defended it. It was bad politics for Mr. Cruz.

Mr. Trump expanded his critique into a full-blown issues platform. In a Wall Street Journal op-ed, five days before the New York primary, Mr. Trump argued that the old order, the governing elite, the establishment, and the special-interest donors, consultants, pollsters, and pundits are the same people “who were wrong on taxes, on the size of government, on trade, on immigration, on foreign policy.”

In clear terms Mr. Trump connected Mr. Cruz with exactly those establishmentarian elites who have bred so much anger and resentment in Republicans everywhere. He completely outflanked Mr. Cruz while turning a process issue into a policy issue. The more Mr. Cruz defended the delegate process, the more Mr. Trump hammered away at his new theme that Cruz is defending the elite old order. In that Journal op-ed, Mr. Trump charged that Mr. Cruz is actually a member of the very “Washington cartel” that the Texan criticizes.

Like other state primaries forshadowed, the New York exit polls showed that 88% of voters were either dissatisfied or angry at government, while 64% wanted a president who was outside the political establishment.

Much of this may be unfair to Mr. Cruz’s issue positions and beliefs, but the distinguished senator, in his defense of the status quo delegate process, made a strategic error. Heading into yet another Super Tuesday, Mr. Trump is making sure that the Mr. Cruz error is compounded and magnified.

By turning delegate caucus defeats into an overall message victory, Mr. Trump has given himself a leg up for the GOP nomination that is — how to put it? — yuge.