Senator Jeff Flake (R-AZ) issued a stern warning to President Donald Trump on Tuesday not to fire Special Counsel Robert Mueller, for doing so would result in impeachment.

We are begging the president not to fire the special counsel. Don't create a constitutional crisis. Congress cannot preempt such a firing. Our only constitutional remedy is after the fact, through impeachment. No one wants that outcome. Mr. President, please don't go there.

There are growing concerns in Washington that Trump is preparing to, or at the very least, considering finding a way, to fire Special Counsel Robert Mueller.

Mueller's investigation into Russian election meddling has budded off into a potential obstruction of justice case against the president, as well as possible financial crimes committed by the Trump Organization and its associates.

Despite his plea to the president and threat of impeachment, however, Flake, who sits on the Senate Judiciary Committee and is considered by some to be a potential presidential candidate in 2020, has declined to support legislation that would protect Mueller from being fired in the first place.

Flake told reporters on Monday that he questioned the constitutionality of a law that would protect Mueller from the president's wrath.

"It needs to be constitutional, and we're trying to explore that. I'm not convinced that's what's been introduced so far is constitutional."

Nevertheless, Flake's message to Trump is the most aggressive warning issued to the president by any Republican thus far. What would normally be a politically risky move is mitigated by Flake's intention to not seek reelection in the 2018 midterm elections.

In an interview with The Washington Post, Flake compared the current drama to the Watergate scandal.

If (Trump) fires (Mueller) without cause, how different is that from what Nixon did with the 'Saturday Night Massacre'? He left before impeachment came, but that was the remedy then and that would be the remedy now.

The White House maintains that Mueller is not in danger of being fired. "The President is not considering or discussing the firing of special counsel Robert Mueller," White House Press Secretary Sarah Huckabee Sanders told reporters on Tuesday.

But as we've seen so often in his presidency, Trump likes to go rogue and follow his gut, usually much to the chagrin of his advisers and legal counsel. Flake also said in the WaPo interview that the president should be cognizant of the implications of his actions.

The president needs to be reminded that while there is nothing the House and the Senate can do constitutionally to prevent the president from moving forward, our remedy is on the other side. And the firing of a special prosecutor without cause will, as Lindsey Graham said, prompt that remedy.

On Friday, the president once again called the Russia investigation a "WITCH HUNT," and that the whole thing was Hillary Clinton's fault.

For a witch hunt, however, Mueller certainly is finding lots of witches. So far, 19 people have been indicted for crimes relating to election meddling and related financial crimes.

Over the weekend, Trump targeted Mueller in a tweet, implying that the entire investigation is a sham perpetrated by Democrats. The president wants to know why there are "zero Republicans," which of course is just patently untrue.

Mueller is a Republican. Deputy Attorney General Rod Rosenstein is a Republican. FBI Director Christopher Wray is a Republican.