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President Donald Trump has added a longtime Washington lawyer to his legal team who has publicly promoted a conspiracy theory that officials in the FBI and Justice Department are plotting to frame the president with a "false crime" in the Russia investigation.

Joseph diGenova, a former U.S. attorney for the District of Columbia, recently joined Trump's legal team, Jay Sekulow, one of the president's lawyers, confirmed to NBC News Monday.

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"I have worked with Joe for many years and have full confidence that he will be a great asset in our representation of the president," Sekulow said in a statement.

DiGenova has strongly touted Trump's claim that the Russia investigation is tainted by bias, with the lawyer telling Fox News in January that there is a secret "brazen plot" by the FBI to "illegally exonerate Hillary Clinton and, if she didn't win the election, to then frame Donald Trump with a falsely created crime."

"The motive would be that they didn't like Donald Trump, they didn't think that he was fit to be president, and they were going to do everything within their power to exonerate Hillary Clinton, and if she lost to frame Donald Trump with a false crime, because they didn't think he should be president," diGenova told the network at the time.

The news comes as Mueller was directly targeted by Trump, who called out the special counsel by name for the first time on Twitter over the weekend and on Monday.

The president characterized Mueller's Russia investigation as a "WITCH HUNT!” and said the probe "should never have been started" because it was "based on fraudulent activities and a Fake Dossier paid for by Crooked Hillary and the DNC, and improperly used in FISA COURT for surveillance of my campaign."

DiGenova declined to comment. His addition to Trump's legal team was first reported by The New York Times.