Donald Trump surrogate and former House Speaker Newt Gingrich (R-GA) said Wednesday that Trump has been “very self-destructive” by hesitating to endorse House Speaker Paul Ryan (R-WI) and Sen. John McCain (R-AZ) in their primaries.

“Let me just say flatly I am totally for John McCain, who is a great war hero and a terrific human being, who has worked very hard for veterans, and I’m totally for Paul Ryan, who is the heart of the House Republican Party and probably the most problem-solving leader we’ve had in the Congress on the Republican side, I think, in the last 20 years,” Gingrich said on Fox Business Network, according to Politico. “So I think somewhat what Trump has done is just very self-destructive.”

Gingrich said that Trump must “find a way to slow down, really learn some new lessons.” And he added that the campaign is a reversal from Trump’s role on his reality television show, “The Apprentice.”

“He doesn’t get to say ‘you’re fired.’ The American people get to say, ‘you’re fired.’ So he’s really got to take a deep breath,” the former speaker said, according to Politico. “I think he has the potential to win the election. I think he has the potential to be a historic president, but to do that, he has got to grow into the size of the job and not get stuck where he has been, which frankly over the last week, I think has been very disheartening to most of his supporters.”

Gingrich said that Trump is in a “slump” and needs to start pivoting to the general election.

“Trump is still behaving like as though it was the primaries and there were 17 candidates. He has not made the transition to being the potential president of the United States, which is a much tougher league,” he said, according to Politico.

Gingrich’s comments come as Trump has made several controversial statements, drawing rebukes from Republicans and his own campaign surrogates. In addition to declining to back Ryan and McCain in the primaries, Trump has launched repeated attacks on the parents of a Muslim American soldier.

Another Trump surrogate, New Jersey Gov. Chris Christie (R), on Tuesday said that Trump’s comments about the Khan family were “inappropriate.”