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But the former counsel, Ken Starr, also told ABC News' "This Week" co-anchor Martha Raddatz that Mueller should “look at” whether Trump lied to the public about wanting to fire the special counsel.
Starr said he takes "very seriously" any possibility that the president may have misled the public when he told reporters last August that he had not even thought of firing Mueller.
As The Washington Post noted, Starr’s investigative report on President Clinton cited his public denial of having sexual relations with Monica Lewinsky as the basis for one of the 11 grounds for impeachment.
"If the reports are correct that President Trump sought to have Mueller fired, then his public denial would be false," Starr said. "So would that be grounds for impeachment?"
"I think lying to the American people is a serious issue that has to be explored. I take lying to the American people very, very seriously," Starr responded. "So absolutely... I think that is something that Bob Mueller should look at."
But Starr maintained that President Trump does have the power to fire Mueller.
“He can ask for Mueller to be fired for any reason," Starr said. "The president's power is extremely broad, as long as he's not engaged in discrimination or accepting bribes.”
Still, Starr said, "It would have been extremely unwise" for Trump to have fired Mueller, as the president reportedly considered doing last June.
Mueller is leading the federal investigation of Russia's alleged interference in the 2016 U.S. election and possible collusion with Trump associates.
Raddatz pressed Starr on whether the president's firing the special counsel would show "corrupt intent."
Starr said the president is "very open" about his feelings on Mueller, his attitude of "'I don't like this guy.'"
Regarding Trump's view of Mueller, Starr said, "I don’t see that as corrupt, I just don’t."
The former independent counsel added, "We just have a Trump Tower set of ethics here, and that is what we’re seeing in the president. I hope that he will control that more in the remaining years of his term. But I think we’re seeing … business tactics. I just don’t see the corruption. He’s so transparent. He tells everyone, 'Look, I want to get rid of this guy.'"