Former CIA Director John Brennan on Tuesday said he believed President Donald Trump was “afraid” of Russian President Vladimir Putin, and speculated that Putin could “have something” of a personal nature on Trump.

In an interview on MSNBC’s “Morning Joe,” co-anchor Willie Geist asked Brennan, a frequent critic of Trump, why the President appeared hesitant to confront Russia over certain issues.

“Do you believe he is somehow in debt to the president of Russia?” Geist asked.

“I think he is afraid of the president of Russia,” Brennan responded.

“Why?” Geist asked.

“Well, I think one can speculate as to why,” Brennan said. “That the Russians may have something on him personally that they could always roll out and make his life more difficult.”

The former CIA director added that “clearly” it was important to improve relations with Russia, “but the fact that he has had this fawning attitude toward Mr. Putin, has not said anything negative about him, I think continues to say to me that he does have something to fear and something very serious to fear.”

“Do you believe Russia has something on him?” Geist asked.

“I believe that the Russians would not–” Brennan hesitated.

“They would opt for things to do if they believe that it was in their interest and the Russians, I think, have had long experience with Mr. Trump and may have things that they could expose and reveal.”

“Something personal, perhaps?” Geist asked.

“Perhaps,” Brennan agreed.

The exchange comes amid the President’s increasingly energetic attacks not against Putin, but against special counsel Robert Mueller. Trump continued complaining about Mueller’s probe of Russian election meddling and related matters on his Twitter account Wednesday.

“Special Council is told to find crimes, whether a crime exists or not. I was opposed to the selection of Mueller to be Special Council. I am still opposed to it. I think President Trump was right when he said there never should have been a Special Council appointed because….. — Donald J. Trump (@realDonaldTrump) March 21, 2018