Republicans who want to stop Donald Trump are rallying behind Senator Rubio. They have the wrong candidate. In two new polls, Mr. Rubio trails Mr. Trump by 16 points and 20 points in Florida, which for the senator is a must-win home-state contest just two weeks away. Mr. Rubio would have a difficult time asking voters in 49 other states to support him if his home state won’t.

Moreover, Mr. Rubio trails Mr. Trump in polls in every state voting in the meantime; winless-ness is hardly the way to build the “Marcomentum” required to close the gap at Florida and become the Trump-tackler.

It is worse than that. Polls suggest that Mr. Rubio may be blanked in the biggest contest of all, this Tuesday in Texas, where the Real Clear Politics average of seven recent polls has Rubio at 18%, just below the 20% threshold to qualify for any of the 155 delegates in the Lone Star State.

That leads to the candidate who could best Mr. Trump, Senator Cruz, who leads Mr. Trump at Texas by 9 points 36 to 28, in the RCP average, and by double digits in the two most recent polls. Mr. Cruz can meet the home-state imperative, and with that big win at his back, can build momentum headed into the winner-takes-all phase of primary season which begins March 15.

Otherwise, is Mr. Cruz a stronger candidate than Rubio? Yes, starting with the fact that he has more money. The last official campaign funding reports, dated January 31, showed Mr. Cruz and his super-PACs with $40 million in the bank versus $10 million for Mr. Rubio and his super-PACs.

Ironically, the central reason that Mr. Cruz can stop Trump is reflected in the response of many anti-Trump Republicans when you suggest Cruz. They say “What’s the difference?” The stop-The-Donald crowd misses the central lesson of this election cycle, namely that GOP voters are furious at “the establishment” and yearning for someone to reassert national pride and patriotism. Call this Trumpism. Mr. Cruz best embodies it.

That Senate colleagues “despise” Mr. Cruz serves as his best endorsement for angry GOP primary voters. Rubio doesn’t have that kind of credibility.

Now is there a difference between Mr. Cruz and Mr. Trump on matters of character and capability? Mr. Trump and his insults are in a class of their own. Mr. Rubio, moreover, has gone into the gutter with Mr. Trump in the last few days, while Mr. Cruz has stayed above the fray.

The accusations that Mr. Cruz’s campaign used “dirty tricks” is proving inaccurate. The original charge was that his campaign spread false news on the eve of the Iowa caucuses that Ben Carson was dropping out of the race. Actually, Cruz operatives saw a CNN reporter’s tweet that, after the caucuses, “Carson won’t go to NH/SC, but instead will head home to Florida for some R&R.”

They contacted Cruz supporters and urged them to tell Carson supporters that he was “suspending campaigning” and to try to win them over. Jake Tapper and Dana Bash commented on air that the suspension was “very unusual.” Elsewhere CNN and the Carson campaign clarified that Carson was not dropping out. The Cruz campaign didn’t clarify.

The controversy abated when it turned out that Dr. Carson did go home for three days, which, in the rush of primary contests, which was the equivalent of dropping out of the race, as Ms. Bash observed “If you want to be president of the U.S., you don’t go home to Florida.”

The Donald may (or may not) have an impressive record as a businessman, but Mr. Cruz enjoys a stellar reputation in the law. He has argued nine cases before the Supreme Court, including an astonishing showdown known as Medellin, in which Mr. Cruz, then solicitor general of Texas, defeated attempts by the International Court of Justice and the President of America to use a technicality under an international treaty to overturn the convictions of 51 Mexican nationals of murder in Texas. This was a seminal victory of American law over the creep of international law and globalism, something which offends most Republicans.

Compared to Mr. Rubio, Mr. Cruz has run a better campaign. The Texan has lined up endorsements of both the incumbent governor of his state, Gregg Abbott, and his predecessor, Rick Perry, while Mr. Rubio has had to watch Governor Scott flirt with Mr. Trump.

Establishment Republicans may not like that Mr. Cruz has run a campaign lambasting them, but they have to concede that Mr. Cruz has read the mood of the voters. They may consider Mr. Cruz’s preparedness to shut down the government unproductive, or even counter-productive, but that was a disagreement over tactics, not the substantive issues: Obamacare, the Iran deal, Obama’s executive orders on illegal immigration.

In the CNN debate in Las Vegas in December, Hugh Hewitt asked Trump about the nuclear triad of strategic bombers, inter-continental missiles, and submarine-based weapons. The Donald answered in a way that indicated clearly that he did not know what the triad is.

Again, many Republicans who want to stop Mr. Trump, say of Mr. Cruz “What’s the difference?” As to Trumpism, little. As to the men, much. If Republicans want to stop Mr. Trump, the crucial difference is the one between Messrs. Cruz and Rubio. Mr. Rubio can’t stop Mr. Trump; Mr. Cruz can.

Mr. Jahncke is president of The Townsend Group Intl, LLC. RTJahncke@Gmail.com.