Corey Lewandowski said former Vice President Joe Biden might have important knowledge about the Obama administration's efforts to surveil the Trump campaign during the 2016 election and the use of an unverified dossier to obtain Foreign Intelligence Surveillance Act warrants.

During an interview on Fox Business, President Trump’s former campaign manager said Democrats "should be fearful" of Justice Department Inspector General Michael Horowitz's FISA abuse investigation, which is expected to wrap up in the next couple weeks.

Lewandowski specifically called out Biden, who is now the front-runner for the 2020 Democratic presidential nomination.

"The person who has gotten a pass on this so far is Joe Biden, because I believe that the investigation, which was launched, came from somewhere inside the White House to green light Clapper, Comey, and Brennan to start this investigation into Donald Trump for no valid reason," Lewandowski said on Thursday. He was referring to former Director of National Intelligence James Clapper, former FBI Director James Comey, and former CIA Director John Brennan.

Lewandowski touched on the revelation that the State Department notified the FBI that the author of the dossier, British ex-spy Christopher Steele, had credibility issues before the bureau used his research to obtain FISA warrants against onetime Trump campaign adviser Carter Page. He appeared to confuse the July 2016 start of the counterintelligence investigation into the Trump campaign, code-named Crossfire Hurricane, with the FBI applying for its first FISA warrant against Page in October of that year.

[Also read: Biden prepares to blast Trump over Russia, a threat he dismissed in 2012]

"This person had no credibility, but it continued because it came from the highest levels of the government," Lewandowski said. "Joe Biden has not answered what he knew and when he knew it of how this investigation began."

Lewandowski also said he expects Comey, and other former FBI personnel to be subject to criminal referrals and be on trial by March or April of next year.

The interview took place soon after Trump gave Attorney General William Barr "full and complete authority to declassify information" related to the origins of the federal investigation into possible ties between the Trump campaign and Russia.

Lewandowski is a vocal supporter of Trump and his administration. In 2018 he joined Vice President Mike Pence’s Great America PAC.