Arizona Republican Rep. Trent Franks is calling on former FBI Director Robert Mueller to resign as the special counsel investigating Russian interference in the 2016 election.

In a news release, Franks cited Mueller’s longstanding friendship with James Comey, who was fired as FBI director by President Donald Trump in May, as a conflict of interest.

“Bob Mueller is in clear violation of federal code and must resign to maintain the integrity of the investigation into alleged Russian ties,” Franks said, citing a Fox News story on Comey and Mueller’s friendship.

Franks also repeated a growing right-wing criticism that Mueller is acting in a partisan manner because some of the special counsel’s team contributed to Democrat Hillary Clinton’s presidential campaign.

“These obviously deliberate partisan hirings do not help convey impartiality,” he said.

Franks’ criticism mirrors that of former House Speaker Newt Gingrich, who called Mueller’s investigation a “one-sided political witch hunt,” as well as Trump, who complained in a Fox News interview that Franks cited in his statement.

“Until Mueller resigns, he will be in clear violation of the law, a reality that fundamentally undermines his role as Special Counsel and attending ability to execute the law,” Franks said.

Franks’ sentiments come as Trump has called the Russia investigation 
“the greatest witch hunt in political history.”

Trump has also been critical of Attorney GeneralJeff Sessions for recusing himself from the Russia investigation, which led to Deputy Attorney General Rod Rosenstein appointing Mueller as special counsel.