Sen. Jeff Flake, R-Ariz., is calling on his colleagues in the Senate to "stand up" and be "more forceful" in light of President Trump's most recent behavior as commander in chief.

"I think we have a responsibility as elected officials to speak out when there's behavior that goes beyond the pale and some of what we've seen fits in that category," said Flake of Mr. Trump on "CBS This Morning."

When asked if Congress should ever expect a change out of the Oval Office, Flake replied, "We've been waiting nine months for that pivot to occur toward more appropriate behavior and stability and we haven't seen it. It's time we stand up and be a little more forceful."

Flake abruptly announced on Tuesday that he won't run for re-election in the 2018 midterm elections and will leave the Senate when his term ends in January 2019. He also delivered a blistering rebuke of Mr. Trump's behavior.

The Arizona Republican announced on the Senate floor that he could "better serve my country and conscience" by dropping his re-election bid, "freeing myself of the political consideration that consumed far too much bandwidth."

He also penned a blistering op-ed in the Washington Post published on Wednesday, where he compared the political climate to that of the McCarthy era in the 1950s.

"This was a time when McCarthy had gone on for a couple of years and done a lot of damage and no one was willing to speak up," Flake wrote of that time in Congress.

He added, "Until this time, this hearing, when Chief Counsel for the Army Joseph Welch stood up, that really turned things around. At that point that was the threshold that I guess we had to get to, things changed after that."

Asked what Flake suggests should happen next after rebuking the president's actions on the campaign trail and his time in office, Flake stopped short of suggesting Mr. Trump being removed from office.

"I don't think any of those remedies are justified, high crimes misdemeanors, impeachment. I don't think that's the way to go," said Flake.

He suggested, however, that members of Congress "ought to speak out when the president follows through on some of the threats he's made," particularly as it relates to the First Amendment.

"If he continues to, in terms of the tweets and just the debasing statements he's made and also on the foreign stage, I think we need to be incredibly careful about what we're doing," he added.

Flake's dramatic announcement came just hours after Mr. Trump met with Senate Republicans on Capitol Hill and after his Republican colleague Sen. Bob Corker of Tennessee also took the president to task, furthering their ongoing feud.

His declaration on leaving the Senate also comes after former White House strategist Steve Bannon rallied behind Flake challenger Kelli Ward, in an effort to help elect anti-establishment candidates.

When Flake announced his intentions not to seek reelection, Breitbart, Bannon's news outlet, posted "WINNING" 14 times in a row in a single tweet.

Flake issued this warning to Congress: "I do think that the longer we go, the more this behavior is normalized and that is a problem we can't allow our dialogue to continue to worsen and so it think the longer we wait the more likely that is, already we're seeing the effects of this new era and they've not been good."

Flake said while he's spoken with his colleagues who have not been as vocal against the president, he expects to see "a lot more people stand up" in the future.