Sen. Ted Cruz (R-Texas) wrote on Facebook on Friday that he plans to vote for Donald Trump, even though he declined to endorse him at the Republican National Convention.

“In Cleveland, I urged voters, ‘please, don’t stay home in November. Stand, and speak, and vote your conscience, vote for candidates up and down the ticket whom you trust to defend our freedom and to be faithful to the Constitution,'” Cruz posted on his Facebook page.

“After many months of careful consideration, of prayer and searching my own conscience, I have decided that on Election Day, I will vote for the Republican nominee, Donald Trump.”

During a brutal primary campaign, Trump had referred to Cruz as “Lyin’ Ted Cruz,” and have even cited a National Enquirer story that linked Cruz’s father to Lee Harvey Oswald. The day after the convention, Trump said, “All I did was point out the fact that on the cover of the National Enquirer, there was a picture of him and crazy Lee Harvey Oswald having breakfast. Now Ted never denied that it was his father.”

For his part, Cruz said that he declined to support Trump because “I am not in the habit of supporting people who attack my wife and attack my father.” As he spoke at the convention, he was booed as it became clear that he would not offer his endorsement. During the primary, he had called Trump a “pathological liar” and “utterly amoral,” among other things.

But on Friday, Cruz wrote that he had “made this decision for two reasons. First, last year, I promised to support the Republican nominee. And I intend to keep my word.

“Second, even though I have had areas of significant disagreement with our nominee, by any measure Hillary Clinton is wholly unacceptable — that’s why I have always been #NeverHillary.”

Cruz then went on to list six policy differences between Trump and his rival Hillary Clinton that earned Cruz’s endorsement. “If Clinton wins, we know — with 100% certainty — that she would deliver on her left-wing promises, with devastating results for our country,” Cruz added.

Trump and Clinton will have their first presidential debate on Monday, Sept. 26.

Trump said in a statement, “I am greatly honored by the endorsement of Senator Cruz. We have fought the battle and he was a tough and brilliant opponent. I look forward to working with him for many years to come in order to make America great again.”

Cruz is widely viewed as a presidential contender in 2020 or 2024, but Republican National Committee chairman Reince Preibus recently warned that those who do not line up behind Trump may face GOP barriers to running for president again.

But other Cruz supporters were dismayed by Cruz’s endorsement.

Rick Tyler, who worked as his communications director, told NBC News’ Hallie Jackson,  “It’s mourning in America for conservatives. We lost our leader today.”