Sen. Jeff Flake said Sunday it was a “horrible day for democracy” when Andrew McCabe was fired as deputy director of the FBI, and suggested President Trump is preparing to fire special counsel Robert Mueller.

“When the president said it was a great day for democracy yesterday, I think it was a horrible day for democracy,” Flake, R-Ariz., said on CNN’s "State of the Union." “To have firings like this happening at the top, from the president and the attorney general, does not speak well for what's going on.”

Flake, who is retiring this year, added he was concerned Trump is moving to fire Mueller as the leader of the Justice Department probe into Russia’s 2016 election interference, and the potential Moscow collaborated with the Trump campaign.

“I don't know what the designs are on Mueller, but it seems to be building toward that,” Flake said. “And I just hope it doesn't go there, because it can't. We can't, in Congress, accept that. I would expect to see considerable pushback in the next couple of days urging the president not to go there. He can't go there .”

Attorney General Jeff Sessions said he fired McCabe on Friday night for failing to be transparent with the department’s internal watchdog about a conversation he authorized between FBI officials and a journalist. But McCabe, who was fired two days before his planned retirement, said the decision was politically motivated.

Trump has said publicly McCabe should be fired, and celebrated after he was fired.

In the days after McCabe’s firing, Trump has said Mueller’s investigation “should never have been started” and accused the special counsel’s team of political bias.

“I'm just puzzled by why the White House is going so hard at this,” Flake said. “Other than they're very afraid of what might come out. I don't know how you can have any other conclusion.”