Republicans on the House Oversight Committee are having difficulty tracking down a key informant involved in the investigation into President Joe Biden, his son Hunter Biden, and other members of the Biden family, Rep. James Comer, who chairs the committee, said Sunday. "Unfortunately, we can't track down the informant," the Kentucky Republican told Fox News' "Sunday Morning Futures" host Maria Bartiromo. "We're hopeful that the informant is still there. The whistleblower knows the informant. The whistleblower is very credible."