The support of Carson, a famed retired neurosurgeon and author, will likely give Trump a boost with GOP base voters and evangelicals, who embraced Carson’s campaign in its early days and fueled his brief rise to the top of Republican primary polls.

Carson’s decision may surprise some of his backers since Trump made blistering critiques over the past year of stories from Carson’s past. But according to people close to him, Carson has gradually come to see Trump as the GOP’s best chance of winning a general election and turning out droves of disengaged voters.

Appearing Thursday on Fox News radio, Carson hinted that he is “certainly leaning” toward a candidate and spoke highly of Trump.

“There’s two Donald Trumps. There’s the Donald Trump that you see on television and who gets out in front of big audiences, and there’s the Donald Trump behind the scenes,” he said. “They’re not the same person. One’s very much and entertainer, and one is actually a thinking individual.”