Ted Cruz was booed after he failed to endorse Donald Trump as the Republican presidential nominee.
Angry supporters chanted "We want Trump!" and "Endorse Trump!" during angry and chaotic scenes at the party's national convention.
Our Washington Correspondent Robert Moore sent this analysis from Cleveland.
I have never seen anything like this.
A party convention is meant to be an exercise in political discipline, marketing, and messaging. Above all, it is meant to be a raucous display of unity and enthusiasm.
But instead of cohesion there was chaos on the floor of the Republican convention in Cleveland.
Next to me, two delegates were involved in a scuffle. There were arguments breaking out everywhere. Ted Cruz, the senator from Texas who was the last challenger to Trump, came onto the stage to speak.
Instead of endorsing Trump, he bravely - or perhaps foolishly - told delegates the opposite. "Vote your conscience," he declared. Those three words are code for: Abandon Trump and don't fall for a fraud.
Cue, jeers and whistles.
Cruz left the arena scorned and humiliated. His wife Heidi had to be taken to safety by security staff.
The Republican Party was rupturing in front of our eyes. Delegates were left completely divided.
One delegate from Texas, Mike Goldman, told me that Cruz's refusal to endorse Trump was the greatest act of political courage he had ever witnessed.
But many more were furious, accusing Cruz of throwing the party under the bus in pursuit of his career.
Through all of the political tumult, Donald Trump looked serene. His big moment comes later tonight. He must somehow build a bridge between the warring factions.
I have the sense he won't even try.
Trump believes he can break all the rules of the Presidential game. He will follow the script of the last 12 astonishing months: Let Trump Be Trump.
He will rouse his supporters, attack Hillary Clinton, and promise to make America great again. It will make for riveting high-stakes television.
This is the greatest drama we've seen in a generation in American politics. But is it enough to take him from Trump Tower to the White House?