Rep. Peter King, R-N.Y., said he is “confident” that when Attorney General Bill Barr concludes his investigation of the origins of the investigation of President Trump’s 2016 campaign, the American people will learn that the FBI and CIA under the Obama administration engaged in foul play.

President Trump and his supporters have questioned how the investigation started in the first place, accusing the FBI of carrying it out under false pretenses. King is among those leveling such allegations.

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“There was no legal basis at all for them to begin the investigation of his campaign,” King said in a Friday interview with New York radio host John Catsimatidis, “and the way they carried it forward and the way information was leaked, the improper applications they filed in the FISA court to get surveillance, all of this is going to come out.”

King was referring to the FBI’s application for a warrant under the Foreign Intelligence Surveillance Act to monitor former Trump campaign adviser Carter Page. Republicans, including California Rep. Devin Nunes, claimed that federal authorities did not fully disclose their reliance on an unverified dossier compiled by Christopher Steele, which was part of opposition research for Hillary Clinton’s campaign.

Democrats dispute the notion that anything improper took place. They claim the dossier did not play a major role, and point to a footnote in the warrant application that acknowledged that some of the information came from research on Trump that was likely meant to hurt his campaign, even if it did not spell out exactly who paid for it.

Republicans are now waiting on a report from Justice Department Inspector General Michael Horowitz, following an investigation of possible FBI abuses of the FISA system. Fox News has learned that key witnesses have come forward, after previously holding out.

Sources familiar with the matter said at least one witness outside the Justice Department and FBI started cooperating -- a breakthrough that came after Attorney General William Barr ordered U.S. Attorney John Durham to lead a separate investigation into the origins of the bureau’s 2016 Russia case that laid the foundation for Special Counsel Robert Mueller’s probe.

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But it is not just the FBI that King believes engaged in underhanded tactics. He believes U.S. intelligence was involved as well.

“Just from evidence I’ve seen over the last several years being on the Intelligence Committee, being a member of Congress, there’s no doubt to me there were severe serious abuses that were carried out in the FBI, and I believe the top levels of the CIA,” he said.

A recent RealClearInvestigations report of Mueller's findings pointed to various inconsistencies, as well as the influence of former CIA Director John Brennan, an outspoken critic of President Trump. That report also noted that Mueller's team did not personally investigate the hacking of Democratic National Committee emails, but used a DNC contractor to determine that Russia was behind it.

King is no longer on the House Intelligence Committee, but current members will have an opportunity to ask Mueller about this when he testifies before the committee on July 17.

Mueller was subpoenaed by Democrats, who have discussed impeaching Trump over evidence in Mueller’s report they believe support a case for obstruction of justice. Republicans, meanwhile, are looking forward to asking Mueller about the origins of the investigation, as well as exactly when Mueller determined that the evidence did not support claims that Trump’s campaign conspired with Russia.

Fox News' Catherine Herridge and Cyd Upson contributed to this report.