But a speech designed by the Texas senator to lay the groundwork for a future bid at the presidency quickly unraveled as the crowd met Cruz with resounding boos after he withheld his endorsement of Donald Trump as the Republican nominee.

Cruz, the runner-up in the 2016 Republican primary, had arrived onstage to a thunderous reception at the arena in Cleveland. The senator, who clashed bitterly with Trump prior to suspending his presidential campaign in May, congratulated his former opponent for the first time on winning the party’s nomination and appeared to extend an olive branch to Trump’s supporters.

“Like you, I want to see our principles prevail in November,” Cruz told the thousands gathered.

But the mood within the arena changed dramatically when Cruz, while delivering what sounded like the opening speech of a second presidential campaign, declined to make the case for Trump’s election.

“Please, don’t stay home in November,” he said. “Stand, and speak, and vote your conscience, vote for candidates up and down the ticket who you trust to defend our freedom and to be faithful to the Constitution.”

Factions of the audience had already grown impatient, drowning Cruz out with jeers and chants of “Trump! Trump!” as he spoke at length with an impassioned pitch for conservative values without making a single mention of the Republican nominee.

Cruz at first made light of the protests, telling the crowd: “I appreciate the enthusiasm of the New York delegation.” It was a reference to his infamous skirmish with voters in Trump’s home state, whom the senator had knocked during his campaign as holding “New York values”.

The crowd nonetheless appeared to be holding out hope for a last-minute change of heart, even as aides to Cruz had repeatedly cautioned he would not be endorsing Trump in his speech.

Cruz instead issued a lengthy rebuke of Barack Obama, criticizing the president’s record on domestic issues and foreign policy. He also addressed the heightened tensions among Americans amid frayed race relations, before making an appeal for new leadership in broader terms.

“We’re not fighting for one particular candidate or one particular campaign,” Cruz said.

“We deserve leaders who stand for principle, unite us all behind shared values, cast aside anger for love. That is the standard we should expect, from everybody.”

But as it became clear Cruz would not be backing Trump, most of the crowd revolted and drowned out the final moments of his speech with boos that reverberated across the basketball arena. Cruz put on a brave face, wrapping up his remarks and thanking the audience, but the damage had been done. In the midst of the uproar, Heidi Cruz had to be escorted out by security due to fears for her safety.

As the convention broke for the night, Trump accused his former rival of failing to honor a pledge all the GOP candidates had made to support the eventual nominee:

Republican officials told reporters the senator’s speech was “classless”, while commentators observed they had never witnessed anything like before. A moment intended to channel Ronald Reagan’s 1976 convention speech, when the former president revived his political career after failing to win the nomination in his first attempt, was dubbed as memorable for its brutal reaction in an election year already defined by grassroots anger.

Cruz reportedly rejected a last-ditch effort by advisers hoping to persuade the senator to endorse Trump while onstage.

The two men have shared a notoriously frosty rapport following a primary battle that grew uncharacteristically nasty, with Trump attacking the physical appearance of Cruz’s wife, Heidi Cruz, and even implicating his father in the assassination of former president John F Kennedy.

Cruz, on the final day of his campaign in May, let loose his feelings about Trump by assailing his opponent as “a pathological liar”, “a narcissist” and “utterly immoral”.

He was preceded on Wednesday by Florida senator Marco Rubio, who issued an endorsement of Trump through a pre-taped video message that played like a campaign ad.

“After a long and spirited primary, the time for fighting each other is over,” Rubio said.

In a stark turnaround, Rubio also offered full-throated support of Trump as the better candidate on issues such as national security, despite having maintained in recent months that he wouldn’t trust the real estate mogul with the nuclear codes.

Rubio’s absence from the convention was nonetheless notable, given his position as one of the Republican party’s more prominent stars. The senator, who is seeking re-election to the Senate, said he needed to focus on his campaign in Florida.

Rubio, like Cruz, is widely perceived as harboring ambitions to seek the presidency once more.

Neither Rubio or Cruz has ruled out a second presidential bid as early as 2020. Cruz may run regardless of who occupies the White House in four years, an official with the RNC told Yahoo News on Wednesday, predicting the first major challenge to an incumbent president since 1980 if the Texas senator were to stand in a primary against Trump.

Both senators remain keenly aware of the damage they risk inflicting upon their own image by aligning themselves too closely with Trump’s controversial brand of politics. But staring down the barrel at a fractured party, they have taken vastly different routes while picking up the pieces of their failed campaigns.

While Trump’s long-term impact on the party remains unknown, many within the top brass have acknowledged they are bracing for a potentially devastating loss to Clinton in November.

On Wednesday, Cruz crystallized his view that the conservative movement will come to judge those who staked their beliefs on their support for Trump. What will remain to be seen is whether he can deliver on his bet that he will come through to lead the party back to power in 2020, or whether his ambition died in Cleveland.