"I am not in the habit of supporting people who attack my wife and attack my father," Cruz said at a morning meeting where he faced sharp questions from the Texas delegation in Cleveland.
Cruz sensationally withheld an endorsement of Trump in his speech Wednesday, earning a chorus of boos from the floor while getting upstaged in a power play by the GOP nominee himself.
In a dramatic development, as Cruz wrapped up his speech, Trump suddenly appeared in the Quicken Loans Arena in Cleveland. He walked to join his family in a VIP area and flashed a thumbs-up -- a gesture that transmitted clear anger at the Texas senator's behavior.
Cruz, his party's runner-up, uttered Trump's name just once -- to congratulate him -- and instead pitched the ideological brand of conservatism that endears him to the GOP's base.
"I congratulate Donald Trump on winning the nomination last night," Cruz said. "And like each of you, I want to see the principles that our party believes prevail in November."
But as it was clear Cruz was going to end his speech without endorsing Trump, delegates began to boo and some chanted "We want Trump!"
"Don't stay home in November," Cruz said toward the end of his otherwise very well-received speech. "Stand and speak and vote your conscience."
As delegates began to protest, Sen. Cruz's wife, Heidi Cruz, was heckled by Trump supporters shouting "Goldman Sachs!" and escorted out by security. Heidi Cruz, who is an employee of Goldman Sachs, declined to answer questions from reporters, saying, "I don't talk to the media, thanks."
The stunning political theater between the top two contenders in the Republican primary race blew open divisions in the party that the convention is designed to heal, and suggested Cruz believes Trump will lose in November.
Cruz's appearance at the Cleveland convention had been the subject of intense anticipation over his attitude toward Trump, after their intensely personal exchanges in the late stages of the primary race.
He got a prolonged standing ovation as he walked on stage for a speech that appeared to be an attempt to establish himself as the guardian of conservative values that some activists doubt Trump shares.
Blocked from Adelson suite
Cruz's rebuke ignited a hot scene around the senator as soon as he left the stage. People averted their eyes from Cruz and his wife as they walked with their security detail on the skybox level of boisterous Republicans.
On the donor suite level, people approached Cruz and insulted him, a source told CNN's Dana Bash. One state party chair reacted so angrily that they had to be restrained.
Cruz, who has long sought the support of GOP megadonor Sheldon Adelson, was turned away when he tried to enter Adelson's suite.
Andy Abboud, a senior aide to the Las Vegas casino magnate, said Cruz was initially invited to come up to visit the Adelsons, but when he failed to endorse Trump the invitation was rescinded.
"When he didn't endorse, they were stunned and disappointed," Abboud told CNN.
"We could not allow Ted Cruz to use the Adelsons as a prop against Donald Trump," he added. "The Adelsons support Donald Trump and made that clear. They like Ted Cruz, but there was no way the Adelsons were going to be the first stop after not endorsing. That would be disrespectful to our nominee."
Trump did stop by the suite, and Abboud tweeted out a picture of Trump with Sheldon and Dr. Miriam Adelson.
Trump, whose insults of Cruz were a constant on the campaign trail over the past year, tweeted that Cruz didn't honor the pledge GOP candidates had signed to back the eventual Republican nominee.
"Wow, Ted Cruz got booed off the stage, didn't honor the pledge! I saw his speech two hours early but let him speak anyway. No big deal!"
New Jersey Gov. Chris Christie -- a former presidential candidate and now a Trump backer -- blasted Cruz's speech in an interview with Bash.
"I think it was awful," Christie said. "And quite frankly, I think it was something selfish. And he signed a pledge. And it's his job to keep his word."
Trump lawyer Michael Cohen said on CNN that "the only way to describe it is political suicide."
A source close to Cruz said the senator wasn't shocked by the mood after the speech.
"He expected people to not approve," the source said. "Not surprised at the reaction."
Indiana Gov. Mike Pence, who accepted the nomination as Trump's vice presidential nominee at the end of Wednesday's session, sidestepped when asked about Cruz's speech.
"I am just grateful for all the support we are receiving and I am excited about the future," Pence said.
Eric Trump's reaction: "The audience didn't seem to like it right?"
Asked about the impact of the non-endorsement, Eric Trump responded, "I don't think it makes any difference in the world."
Hillary Clinton's campaign seized on Cruz's speech as well, tweeting: "Vote your conscience" with a link to her website.
Delegates unhappy as well: 'He failed the nation'
The reaction from the floor was also swift and harsh.
Newt Gingrich, appearing after Cruz, argued that Cruz's advocacy for constitutionalism meant that he, implicitly, endorsed Trump -- words he himself did not say.
"So to paraphrase Ted Cruz, if you want to protect the Constitution this fall, there's only one possible way and that's to vote the Trump-Pence ticket."
Richard Black, a delegate from Virginia who chaired Cruz's campaign, said after Cruz's speech that it was "doubtful" he would support him again.
"In the end, each individual has a duty to the nation that transcends the duty to themselves,' Black said. "That's where he failed... He failed the nation."
Rep. Trent Franks of Arizona, who backed Cruz, told CNN he was "disappointed" by Cruz' speech.
On him saying "vote your conscience", Franks said, "for the people in this room, a vote of conscience is a Trump vote."
Michigan GOP Rep. Bill Huizenga, a former Marco Rubio supporter, called Cruz' speech "a mistake."
Huizenga said it was also a mistake for the Trump campaign to give Cruz a coveted prime-time speaking slot without some type of "pre-condition" that he would formally endorse Trump.
Jonathan Barnett, a Republican national committeeman from Arkansas, walked off the floor after Cruz's speech.
"He's self-centered. It's all about Ted Cruz. All he did is ruin his political career," Barnett said. "I think he's finished."
Barnett said this is not the kind of grace one shows their party's nominee: "Reagan wouldn't have done that. He endorsed Ford."
Arizona delegate Bruce Ash expressed a similar sentiment.
"Cruz missed his moment. All he had to do was say 'Trump' and he used the dog whistle for 'conscience.' A very disappointing message," Ash texted.
Cruz's difficult challenge
The speech was difficult from the start: Cruz's goal was to walk a tightrope and keep alive his political viability for 2020 without alienating Trump's legion of supporters.
It was the latter that tripped him up.
Cruz came to the dais facing significant pressure to endorse Trump from his campaign aides and surrogates. Yet he is still at a moment of power and relevance: Only 45, a Latino senator who ended his campaign holding onto more political capital than he has ever enjoyed in his career.
His challenge was to remain well-liked in a GOP that, at least for now, is under the control of a man Cruz has indicated that he does not respect. Cruz effectively placed a risky bet that the Republican Party will judge Trump harshly and reward him in the new era for not caving.
"If skillfully played, his stock will rise," Randall Dunning, a Texas delegate who has misgivings about Trump, said the day before he spoke.
Wes Brumit, a Cruz delegate from Texas, defended Cruz's non-endorsement Wednesday night.
"He did mention all the points Trump mentioned: building a wall, fighting ISIS. He just didn't come right out and endorse," said Bumit, who sported a red "Ted Cruz for President" T-shirt and a cowboy hat. "He said everyone should be able to vote their conscience. And that's OK with me."
As for those who loudly booed Cruz? "All the boos were exactly the New York values that Ted has talked about."
Bumit added: "I think Mr. Trump has some things to apologize for to Cruz before Sen Cruz can come onboard fully for Trump."
But the question now is how skillful Cruz played it. If Trump loses narrowly, holdouts like Cruz could be held responsible in 2020 for not unifying the party. And it is clear there are Trump loyalists who now say they are loathe to back him.
Cruz and Trump, once political allies, turned on one another as they became the top two Republicans in the race. And their tension exploded when Trump's associates fanned flames of salacious tabloid rumors about Cruz and later attacked Cruz's father.
Since withdrawing from the race, Cruz has repeatedly declined to endorse Trump, but maintained that he could always come around to backing the Republican nominee. Yet their past tension -- and the personal attacks -- cast a cloud over any accord between the two aspirants.
Cruz's chief strategist Jason Johnson tweeted: "Since it's obvious the shock is contrived, let me ask: What the Hell did they expect from the son of the man who killed JFK? Light'n up."
Former Cruz aide Brian Phillips also defended the senator: "Just more proof this is about submission. We were told for months Trump didn't need Cruz, but when he doesn't endorse they go apoplectic."
The remarkable moment at the convention was the second time Cruz was upstaged by Trump Wednesday.
At a rally on the Cleveland waterfront, as Cruz spoke gingerly to fellow Republicans about "our nominee" and the uncertain future under his former rival, Trump's plane flew in the clear skies behind him.
"That was pretty well orchestrated" Cruz said as the Trump-emblazoned aircraft buzzed through the air and the crowd booed.
Turning to his campaign manager, Jeff Roe, Cruz said, "Jeff, did you email them to fly the plane right when I said that?"