One only has to look at the Frank Luntz focus-group conducted on December 9 to see that attacking Donald Trump is counterproductive and that Texas Senator Ted Cruz is right to not engage Trump with personal attacks or insults. During a Dec. 9, 2015 interview by Bill Hemmer on America’s Newsroom, Ted Cruz explained why he doesn’t engage in personal attacks and insults against the other presidential candidate. You can watch the exchange between Sen. Cruz and Hemmer at the 6:05 mark of this video.

Here’s the transcript of the exchange:

Cruz: Listen from the beginning my approach, not just to Donald Trump but to all of the candidates, is not to engage in personal insults and attacks. You think of the first couple of debates that they just descended into food fights and personal insults back and forth.

Hemmer: You had a very effective comeback that got a lot of headlines. Maybe a more appropriate question is does it change?

Cruz: I like and respect Donald Trump. I don’t anticipate that changing at all.

Hemmer: No?

Cruz: The reason I won’t get engaged in personal insults and attacks, I don’t think the American people care about a bunch of politicians bickering like school children. What they’re interested in is positive real solutions to the great challenges facing this country. That’s why I am working to lead on defending this nation, on standing up to radical Islamic terrorism, on stopping President Obama’s plan to bring tens of thousands of Syrian Muslim refugees.

Hummer: But no critique on Trump?

Cruz: I am grateful Donald Trump is running. And I’ll tell you what, He has helped focus the discussion on securing the border. Border security is national security. I think that’s been very beneficial.

Frank Luntz let a number of reporters watch his December 9 Global dial group as he tested clips of Trump’s speeches and TV appearances, as well as anti-Trump ads. The 29 member focus group all voted for Mitt Romney in 2012 and supported or used to support Trump. After watching the three-hour focus group, Lesley Clark McClatchy Newspapers Washington Bureau White House correspondent, reported that support for Trump intensifies with every provocation. Trump’s supporters are “invested in him and they’re prepared to dismiss every critique.” Many of Trump’s backers would abandon the Republican Party if necessary to support an independent Trump for president.

The Washington Post’s David Weigel reported that the three hours of messaging, venting and friendly arguments revealed the roots of Trump’s support. All that really mattered to the focus group was that the Republican establishment had failed, badly, and that Trump was offering a way out. Participants derided the mainstream media, accusing reporters of covering snippets of Trump quotes when the full context would have validated him. They cited news sources they trusted to refute what they were being told.

Luntz told the group of reporters when the session ended, normally, if I did this for a campaign, I’d have destroyed the candidate after three hours of showing that stuff. Nothing seemed to budge the Trump voters.

According to Weigel, the only issue that moved the panel against Trump was one that evoked memories of the 2012 election. The group was shown an ad in which contractors blamed Trump for the loss of their jobs. That, said one participant, made Trump look less  electable. He downgraded the likelihood of his own Trump vote — from nine out of 10 to just eight.

Asked whom they would back in a three-way election with Rubio, Hillary Clinton and an independent Trump on the ballot, just 10  of the 29 said they would support the Republican nominee. When [mc_name name=’Sen. Ted Cruz (R-TX)’ chamber=’senate’ mcid=’C001098′ ] (R-Tex.) was swapped into the question, a bare majority — 15 — said they would stick with the Republican Party.

Weigel quoted Luntz as saying losing Iowa might help Trump:

“I can’t wait for Iowa, because I now think Ted Cruz will win Iowa. That will be a rallying cry. Losing there might actually help Trump win New Hampshire.”

According to the article about the Luntz focus group in Mike Allen’s Playbook, Luntz told reporters, The participants hate political correctness more than anything else, and that really does stand out to them as a reason to vote for Trump. The participants are also eager to vote establishment Republicans out. Luntz said he thinks some Republican incumbents  will lose because these Trump voters want to send a message so much that they will vote against some of their own candidates. Luntz compares it to Perot back in ’92. But the intensity of support among Trump supporters is far greater than it was for Ross Perot:

“[W]e showed them pro-Trump clips, we showed them anti-Trump clips. … His numbers went up — and up and up. And that’s because it is the people … who are attacking him who lack the credibility. … When’s the last time you saw a Republican … going after opponents, with such viciousness, only to be applauded for being so entertaining? … [T]he longer that this goes, the greater the intensity, the greater the passion, the greater the commitment. And they’re going to be angry as hell. If you think this is angry now, wait and see what happens two months from now.”

Sen. Cruz is right not to engage Trump with personal attacks and insults. To do so is counterproductive. The other Republican candidates would be wise to follow Cruz’ example.