The revelation that Special Counsel Robert Mueller kept secret that a top FBI investigator overseeing the Russia investigation exchanged anti-Trump text messages with an FBI attorney has fueled questions about Mueller’s credibility and his ability to oversee an impartial investigation.

Peter Strzok, the anti-Trump agent, is reported to be the official who first signed the FBI’s Russia investigation into existence and interviewed Michael Flynn. Strzok was also reportedly the one who softened former FBI Director James Comey’s language referring to Hillary Clinton’s email investigation. (BOMBSHELL: Top Clinton Aides Face No Charges After Making False Statements To FBI)

In an appearance on “Tucker Carlson Tonight,” Judicial Watch president Tom Fitton told the Daily Caller co-founder that “both [the Clinton and Russia] investigations in my view have been irredeemably compromised.” (RELATED: Anti-Trump Text Messages Show Pattern Of Bias On Mueller’s Team)

“The Clinton investigation needs to be reopened and the Mueller investigation needs to be shut down until we figure out how badly it’s been politicized,” Fitton said.

The Wall Street Journal’s editorial board said the Strzok news “reinforces our doubts about Mr. Mueller’s ability to conduct a fair and credible probe of the FBI’s considerable part in the Russia-Trump drama” in a column for Tuesday’s paper.

The editors noted Mueller’s close friendship with Comey, as well as his “reluctance to cooperate with” congressional oversight of the Russia investigation.

“The latest news supports our view that Mr. Mueller is too conflicted to investigate the FBI and should step down in favor of someone more credible,” the WSJ editors concluded. “The investigation would surely continue, though perhaps with someone who doesn’t think his job includes protecting the FBI and Mr. Comey from answering questions about their role in the 2016 election.”

In a column for the Washington Post Monday night, conservative radio host Hugh Hewitt called the Strzok bombshell “a blockbuster revelation, carrying the possibility of shattering public confidence in a number of long-held assumptions about the criminal-justice system generally and the FBI and the Justice Department specifically.”

Hewitt called on the Department of Justice to “appoint a special counsel to investigate Strzok’s actions as soon as possible.”

Even before the latest bombshell, former US attorney Andrew McCarthy was already warning about the credibility of Mueller’s investigation, which he said “started out as a fishing expedition.

“The ongoing Mueller probe is not a good-faith investigation of suspected espionage or other crime,” he wrote in National Review over the weekend.

“It is the exploitation of the executive’s intelligence-gathering and law-enforcement powers in order to (a) criminalize Trump political policies with which the Obama administration disagreed and (b) frame Clinton’s electoral defeat as the product of a traitorous scheme rather than a rejection of Democratic-party priorities.”

WATCH: CNN ALLEGES TRUMP BASHING COMEY WON’T HELP BECAUSE SPECIAL COUNSEL MUELLER IS FRIENDS WITH THE FORMER FBI DIRECTOR