Former FBI Director James Comey said Sunday he would have “serious doubts” about President Trump’s credibility as a witness in special counsel Robert Mueller’s investigation of Russia’s election meddling.

Trump and his legal team are debating whether the president should submit to a personal interview with Mueller, who is probing whether the Trump campaign conspired with Russia, and if the president tried to obstruct justice stop to impede the probe.

“I would have serious doubts about his credibility,” Comey said on NBC’s "Meet the Press." “Sometimes people who have serious credibility problems can tell the truth when they realize the consequences of not telling the truth in an interview or in the grand jury would be dire. You would have to go in with a healthy sense that he [Trump] might lie to you.”

Comey would not say whether he would recommend Trump give an interview to Mueller, considering the president's penchant for being loose with facts.

“I hope that he will allow Mueller to complete his work, whether that includes an interview or not is up to him [Trump],” Comey said.

Comey also said he believes Mueller is sensitive to the political calendar, with midterms upcoming later this year, as he works to finish his probe.

“I'm sure he knows all of that,” Comey said. “He is definitely attentive to the calendar. Like all good prosecutors, he wants to finish as quickly as he can.”