The Republican nominee never apologized for his campaign’s attacks on Cruz’s wife and father during the primary, and hasn’t become any more conservative on key policies than he was previously.

Republican insiders say Cruz’s approval numbers have taken a hit since the summer, when he went so far as to pointedly refuse to endorse Trump during a speech delivered from the convention, and that the Texan could be concerned about his 2018 re-election prospects.

Cruz was the runner-up to Trump in the race for the Republican presidential nomination. He declined to back his former rival on ideological grounds and because Trump attacked members of his family down the stretch of their heated primary campaign.

Specifically, the Trump campaign circulated an unflattering photograph of Cruz’ wife, Heidi, and Trump himself suggested that Cruz’s father, Raphael, who immigrated to the U.S. from Cuba, might have been involved in the assassination of President John Kennedy. Trump also had previously floated the conspiracy that Cruz wasn’t eligible to serve as president because he was born in Canada.

Cruz, who cultivated the image of a conservative firebrand who doesn’t back down under pressure, will likely disappoint some of his biggest boosters.

Steve Deace, a talk radio show host in Iowa who endorsed Cruz in the 2016 primary, predicted that endorsing Trump without anything to show for it would diminish his future presidential prospects.

“Ted is still one of the best senators we have. And I hope he’s happy there, because odds he’ll be president severely diminished,” Deace said on Twitter. “I think it’s the worst political miscalculation of my lifetime. I hope I am wrong. The people will decide that.”

Several high-profile Republicans who initially resisted Trump have since endorsed him.