Reporting by Paula Reid

Attorney General William Barr has assembled a team to investigate how the Russia investigation began, a U.S. official told CBS News. Barr said in a Congressional hearing Tuesday that he is "reviewing the conduct of the investigation and trying to get my arms around all the aspects of the counterintelligence investigation that was conducted during the summer of 2016."

Barr's investigation into the origins of the Russia probe, first reported by Bloomberg, is separate from the long-running Office of Inspector General investigation into the Justice Department's handling of the Russia investigation.

There have been concerns within the Justice Department that it is too easy to open an investigation. This stems from the probe into former Attorney General Jeff Sessions after he did not disclose a meeting with the Russian ambassador in 2017. That case was closed, and no charges were filed.

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President Trump has called the special counsel investigation a "witch hunt," and he tweeted in May 2018 that he was demanding the "Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes."

Several congressional Republicans, too, have long questioned the origins of the Russia probe. Sen. Lindsey Graham, a Trump ally, has called on Barr to appoint a special counsel to look into "whether or not a counterintelligence investigation was opened as a back door to spy on the Trump campaign."

This issue is likely to get more attention Wednesday when Barr appears for his second day of testimony before Congress this week, this time before a Republican-led panel in the Senate.

Barr told the House Appropriations Committee on Tuesday that he hopes to release the redacted report by special counsel Robert Mueller "within a week." Barr released to the public a four-page summary of its principal conclusions two days after Mueller submitted his report, but many Democrats have called for the full report to be released.