AUSTIN — Mike Lee wasn't going to let Ted Cruz down. The Utah senator was the first of Cruz's 53 Republican colleagues to endorse him. In June, at the end of a book tour waylaid by questions about Donald Trump, Lee spoke with unusual passion about why he had not endorsed the Republican nominee once Cruz quit the race.

"We can get into the fact that he accused my best friend’s father of conspiring to kill JFK," Lee told Newsmax's Steve Malzberg. "We can go through the fact that he has made some statements that some have identified correctly as religious intolerance. ... I would like some assurances that he is going to be a vigorous defender of the U.S. Constitution, that he is not going to be an autocrat."

Three months later, Cruz (Tex.) endorsed Trump for president — and did not give Lee a head's up. "This Cruz news is all a surprise to us and the senator," his spokesman, Conn Carroll, said.

This was not the first time that Lee's "best friend" had flummoxed him. Lee had appeared blindsided when Cruz, a fellow member of the Judiciary Committee, used a 2015 hearing on criminal justice reform to announce that the threat of "violent criminals" had moved him against a reform bill. "It is simply incorrect to say that this suddenly releases a bunch of violent criminals," said Lee, watching the bipartisan reform effort begin its long, election-year slide into oblivion.

To other conservatives, who had come to see Cruz as a champion of the movement, today's endorsement was just as shocking — and then, suddenly, obvious. Like most of Trump's rivals, Cruz had allowed the mogul's movement to grow inside the Republican Party, expecting the laws of gravity to eventually bring Trump down. When that didn't happen, Cruz became Trump's most bristling, eloquent critic, attacking an "amoral" and "sniveling" candidate who could not be trusted to defend the Constitution.

Cruz's later refusal to endorse Trump at the Republican National Convention got him booed offstage, but won him respect on the right. Glenn Beck, who had campaigned for Cruz across the country, compared him to Sen. Charles Sumner, a 19th-century abolitionist beaten with a cane by a supporter of slavery.

Cruz did call Beck to talk about the Trump endorsement. In a Facebook post, the host said that he had talked to Cruz for 40 minutes, and that the senator would appear on his show Monday to explain himself.

"Profoundly sad day for me," Beck wrote. "Disappointment does not begin to describe. Maybe it is time to go to the mountains for a while."

Other conservatives who had refused to endorse Trump spent the afternoon asking what they'd seen in Cruz. "I think Ted Cruz endorsing Trump at this point plays to the caricature that he is self-interested, not really principled," wrote Erick Erickson, a conservative commentator who had just published a well-received essay on why he still rejected Trump. "Hate it for him." An hour later, he amended his remarks: "It does become almost impossible to claim 'self-interested Ted' is a caricature after this."

Steve Deace, an influential Iowa radio host who campaigned for Cruz, spent Friday afternoon tweeting that he had just seen "the worst political miscalculation of my lifetime," and a genuine, personal disappointment.

"I'm just sorry to see so many people let down again," Deace wrote. "That's the toughest part of this for me. I grow weary of seeing people disappointed. I'm used to being let down. It's a state of being in this line of work. But the people deserve better. I wish I could give it to them."

One thing Cruz learned during the primaries was that the self-identified defenders of true conservatism did not have as much pull as  it seemed. Cruz sought and won endorsements from some of the strongest voices in the movement, from Beck to Mark Levin to James Dobson to Robert P. George. On the trail and in debates, he (eventually) cast Trump as an ideological phony, a donor to Democrats — including Hillary Clinton — who could not be trusted.

"It's easy to say 'Make America Great Again,' " Cruz said in one often-repeated riff. "Why, you can even put that on a baseball cap! The question is, do you understand what it was that made America great in the first place?"

Most Republican primary voters tuned this out. Most delegates booed when Cruz suggested that there were principles keeping true conservatives from backing Trump. When Cruz refused to endorse Trump at the RNC, and an angry Texas delegation (composed mostly of Cruz delegates) gave him an earful, Cruz pivoted to the personal, saying that Trump had insulted his family.

"That pledge was not a blanket commitment that if you go slander and attack Heidi, then I'm going to nonetheless come like a servile puppy dog and say thank you very much for maligning my wife and maligning my father," Cruz said.

Today, both explanations for his long hold-out came back to haunt Cruz. By buckling, Cruz was suggesting that Trump had failed ideological tests and it hadn't mattered, and that it didn't really matter that Trump had smeared his wife and father.

"With his endorsement of Donald Trump, a man who humiliated his wife and father, Ted Cruz is the literal definition of a cuckservative," wrote Jamie Kirchick, an anti-Trump conservative columnist.

"Cruz's conscience told him he must vote for a man who mocked the looks of his wife and falsely connected his father to the JFK assassin?" asked Stephen F. Hayes, a Weekly Standard columnist.

And it didn't escape notice that Trump had mocked the idea of Cruz endorsing him. "I don't want his endorsement," Trump had said after the convention snub. "If he gives it, I will not accept it." Today, a rote news release informed reporters that Trump was "greatly honored" by the endorsement.

It was a reminder that Cruz had been humbled by the convention's aftermath. In Gallup polls, his favorable rating with Republicans, already lower than Trump's, tumbled 20 points. More important, donors who had bet on Cruz excoriated him for not being a Trump team player. "We need ‘all hands on deck’ to ensure that Mr. Trump prevails," said the mega-donors Robert and Rebekah Mercer to the New York Times. "Unfortunately, Senator Cruz has chosen to remain in his bunk below, a decision both regrettable and revealing."

Cruz, who is up for reelection in two years, had no easy way to reunite conservatives behind him. Some Texas Republicans were urging Rep. Michael McCaul, the second-wealthiest man in Congress, to primary him; the Mercers were suggesting that Cruz could look elsewhere for help.

Still, in the Facebook message that explained his conversion, Cruz provided a series of strong policy arguments for backing Trump. Either he or Clinton was going to win the election. Cruz, whose Washington career began when he was the clerk for Chief Justice of the United States William H. Rehnquist, explained that the fate of the Supreme Court was a strong reason for staying with Trump.

"I have been seeking greater specificity on this issue," wrote Cruz, "and today the Trump campaign provided that, releasing a very strong list of potential Supreme Court nominees — including Sen. Mike Lee, who would make an extraordinary justice — and making an explicit commitment to nominate only from that list. This commitment matters."

But a few hours had passed between Trump's release of the list and Cruz's statement. In that time, Lee's spokesman had already declined any interest in a Supreme Court nomination.

"Sen. Lee already has the job he wants," Conn Carroll said.