The FBI has fired Peter Strzok over anti-Trump text messages he exchanged with his lover during the 2016 presidential campaign, Strzok's lawyer Aitan Goelman confirmed Monday.

Strzok, who led the FBI's investigation into Russia's interference in the 2016 election, was fired on Friday on the orders of FBI Deputy Director David L. Bowdich, Goelman said. The decision overruled a previous decision from the FBI's office of professional responsibility that found Strzok should face a demotion and 60-day suspension.

"This decision should be deeply troubling to all Americans," Goelman said in a statement Monday. Goelman accused Bowdich of bowing to political pressure and said the firing was not based "on a fair and independent examination of the facts."

The FBI has also confirmed the firing of Strzok.

"Mr. Strzok was subject to the standard FBI review and disciplinary process after conduct highlighted in the IG (inspector general) report was referred to the FBI's Office of Professional Responsibility," the agency said in a statement to CNBC.

The FBI issued its decision to fire Strzok after reviewing the investigative materials and the responses of Strzok and his counsel, the statement said.

President Donald Trump took to Twitter to celebrate the news, and speculated about whether special counsel Robert Mueller's Russia probe will be "dropped." Mueller removed Strzok from his team in the summer of 2017 after he became aware of the text messages.

"Agent Peter Strzok was just fired from the FBI - finally," the president wrote Monday. "The list of bad players in the FBI & DOJ gets longer & longer. Based on the fact that Strzok was in charge of the Witch Hunt, will it be dropped? It is a total Hoax. No Collusion, No Obstruction - I just fight back!"

Trump tweet

Strzok has been a target of withering criticism since text messages he exchanged with FBI lawyer Lisa Page became public. In thousands of messages, Strzok and Page disparage the president and other political figures.

In one exchange, Page asked Strzok: "Trump's not ever going to be president, right? Right?!"

In response, Strzok wrote, "No. No he won't. We'll stop it."

That text exchange was one of 40,000 reviewed by the Justice Department's inspector general in the course of its review of the investigation into former Democratic presidential contender Hillary Clinton's private email server. Strzok played a senior role on the Clinton email investigation.