CLEVELAND — In a dramatic act of political risk and defiance, Sen. Ted Cruz of Texas refused to endorse Donald Trump during his speech here Wednesday night, earning a thunderous round of boos from delegates that will go down as one of the most memorable and raucous moments of the Republican National Convention .

Cruz's decision to tell Republicans to follow their conscience – rather than explicitly vote for the Republican nominee this fall – was a gutsy but potentially ruinous choice that will define his future.

The runner-up for the 2016 GOP nomination clearly wants to seek the presidency again, yet Wednesday's roll of the dice might make his path back impossible.

Cruz began his speech by congratulating Trump for winning the nomination and explaining that he hoped to see the principles of the GOP succeed. He went on to embrace some of Trump's policies, including the building of a wall along the border with Mexico.

But as he continued to talk about a litany of principles and favorite issues, tension built in Quicken Loans Arena. Would he ever get around to endorsing Trump?

Delegates on the floor became so irritated at Cruz that they began chanting over him, "Trump! Trump! Trump!"

Cruz stopped and grinned through it, and then took a dig at the state that punished him so badly in the primary.

"I appreciate the enthusiasm from the New York delegation," he said.

That earned only more boos. One delegate muttered, "Come on, endorse him."

Cruz did not budge. Trump, seated with his family, looked dour and walked out of the floor box.

Heidi Cruz, the senator's wife, was reportedly escorted out as frustrated Trump delegates began heckling her and yelling, "Goldman Sachs!"

Cruz's was a stand on principle, one that will energize his hardcore supporters and endear him to those who find Trump to be a figure without an ideological rudder. Those who believe Trump will go down in flames this fall will point to this moment and say Cruz fell on the right side of history.

But the move also will open the first-term Texas senator up to charges that he is a sore, self-centered loser who injured the party's nominee during a crucial, nationally watched event designed to foster unity.

If Trump loses to Hillary Clinton in a close contest, Cruz could be fingered as partly to blame, given that he gave permission to his followers to abstain from the presidential race. Yet the reverberations of his choice are only beginning.

Inside a donor suite later, Cruz was called a "disgrace" and security had to restrain a man, according to CNN.

Democrats delighted in the disarray unfolding, but also sympathized with Cruz's plight.

"But to be fair, would you want to endorse a guy who threatened to 'spill the beans ' on your wife and accused your dad of maybe killing JFK?" read a press release from the Clinton campaign.

Picturing the RNC View All 58 Images

While Cruz settled on a spectacular shun, another former Trump rival with eyes on another White House try – Wisconsin Gov. Scott Walker – took a vastly different approach.

Walker was also once a ferocious critic of Trump, and said last year when dropping out of the race that he wanted to help unite the party and stop him.

But on Wednesday night, he signed on, repeating a mantra that "America deserves better."

"So let me be clear: A vote for anyone other than Donald Trump in November is a vote for Hillary Clinton," Walker said.

Walker saluted like a traditional party leader would, his calculation being that even if Trump loses the general election, his voters aren't going anywhere. And they'll remember who backed the nominee when the time came.

Walker chose the more customary path for a former rival, whereas Cruz essentially ignited a blood war.

The irony in this is that during the GOP primary campaign, Cruz was one of the last of Trump's competitors to criticize him. He snickered that while the liberal media would love to cover a Cruz-Trump throwdown, he wouldn't oblige.

Privately, Cruz's campaign command believed that Trump eventually would collapse and that their candidate would naturally inherit his support. But the Trump implosion never came, and Cruz was eventually forced to strike at The Donald in debates on the trail.

That led to weeks of contentious back-and-forths in which Cruz dubbed Trump "a pathological liar" and Trump nicknamed Cruz "Lyin' Ted."

Several other former rivals of Trump – like Jeb Bush and South Carolina Sen. Lindsey Graham – have refused to get behind him, but they also aren't speaking at the Republican National Convention.

What Cruz pulled off was so astounding because he was able to speak to the convention in a prime-time hour without backing the nominee.

Both Trump and a Cruz strategist said the nominee knew of Cruz's plans ahead of time – Trump tweeted that he saw the remarks early and "let him speak anyway" – though perhaps Trump figured the senator would come around and help him bring the party together in the end.

One thing that's known for certain: Trump doesn't take slights like this easily.