A federal judge rejected claims by a former top FBI counterintelligence agent who had a key role in the “Russiagate” investigation and called President Trump a “loathsome human” in a private text message that his 2018 firing violated his First Amendment rights.

Peter Strzok, who also led the FBI’s investigation into Secretary Hillary Clinton’s use of a private email server, argued in his 2019 lawsuit that the FBI fired the 25-year FBI veteran due to “unrelenting pressure from President Trump” after text messages between him and an FBI lawyer, Lisa Page, were brought to light.

In her order, U.S. District Judge Amy Berman Jackson dismissed the suit, ruling that his interest in expressing his opinions did not outweigh “the FBI’s interest in avoiding the appearance of bias in its ongoing investigations of those very people.”

Judge Jackson also found that Mr. Strzok failed to prove that he was penalized more harshly because the target of his criticism was Mr. Trump. 

“Each of the FBI officials deposed maintained that given plaintiff’s rank and his role in the two investigations, and the appearance of bias that permeated the messages, the situation was unprecedented, and there were no comparators,” Judge Jackson wrote. 

In the messages — sent while Mr. Strzok and Ms. Page were having an extramarital affair — they referred to Mr. Trump as “abysmal,” “an idiot,” “awful,” and “a disaster.”

In one message exchange, Mr. Strzok, who was overseeing the investigation into possible collusion between Russia and 2016 Trump campaign, wrote to Ms. Page, “And f— the cheating mother—ing Russians. Bastards. I hate them.”

Since then, Mr. Trump has branded Mr. Strzok as proof of the Deep State conspiracy against the president and his allies, calling the former FBI agent “a disgrace to our country.”

In 2017, Mr. Strzok was removed from Special Counsel Robert Mueller’s investigative team after an investigation by the Department of Justice’s Office of Inspector General discovered the text messages. 

In a court filing, government attorneys argued Mr. Strzok’s dismissal was justified because “he exchanged politically charged text messages on his FBI-issued device about individuals who were centrally connected to high-profile investigations.”

In 2019, Ms. Page sued the justice department and the FBI, accusing them of unlawfully disclosing information about her to the media, saying she took “little joy” in doing so.

Last year, both agents reached settlements with the justice department for leaking their text messages to the press. Mr. Strzok and Ms. Page were awarded $1.2 million and $800,000, respectively. Mr. Strzok’s settlement was separate from his First Amendment claims.