A trio of House Republicans asked the federal prosecutor investigating allegations of bias at the FBI and Justice Department during the 2016 presidential campaign for an update on his probe Monday, noting that potential key witnesses have indicated they have not given testimony.

"Your investigation has been ongoing for over nine months," wrote Reps. Jim Jordan, R-Ohio, Doug Collins, R-Ga., and Mark Meadows, R-N.C., to U.S. Attorney for Utah John Huber. "During the course of our extensive investigation we have interviewed more than a dozen current and former DOJ and FBI personnel, and were surprised to hear none of these potentially informative witnesses testified to speaking with you."

Jordan is the top Republican on the House Oversight and Reform Committee, while Collins holds the same post on the House Judiciary Committee.

Former Attorney General Jeff Sessions announced in March 2018 that he had appointed Huber to look into how investigators secured a Foreign Intelligence Surveillance Act (FISA) warrant against former Trump campaign adviser Carter Page, as well as issues surrounding the FBI, the Clinton Foundation and the 2013 sale of Uranium One to a Russian-backed company.

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The letter notes that Huber declined to testify before lawmakers about the Clinton Foundation last month, saying: "We were disappointed to learn from the [Justice] Department you were not enthusiastic about testifying when declining the invitation."

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Jordan, Collins and Meadows have given Huber until Jan. 21 to tell them the number of witnesses he has interviewed as well as those remaining to be interviewed, the number of FISA applications he has reviewed, the total number of documents he has reviewed and "a description and account" of Huber's coordination with Justice Department Inspector General Michael Horowitz.

The Justice Department did not immediately respond to requests for comment.