Washington (CNN) Arizona Republican Sen. Jeff Flake, a chief GOP critic of President Donald Trump, said Sunday he expects pushback from his colleagues over Trump's increased attacks on special counsel Robert Mueller.

"We can't in Congress accept that," Flake said on CNN's "State of the Union," adding, "I would expect to see considerable pushback in the next couple of days."

Trump over the weekend tweeted that the Mueller probe into Russian meddling in the 2016 election never should have begun, and on Sunday morning, continued to rail against the ongoing investigation. Trump attorney John Dowd said in a statement on Saturday that he hopes Deputy Attorney General Rod Rosenstein, who appointed the special counsel, will end the investigation.

When asked if he really felt GOP leaders, like Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan, would come to Mueller's defense, Flake said, "I hope so."

"I mean, talking to my colleagues all along it was, you know, once he goes after Mueller, then we'll take action," Flake said.

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