McCain ended up passing it off to a congressional liaison rather than dealing with it as a ranking member of Homeland Security and Governmental affairs committee, and the Investigations subcommittee.
Here’s the official response to McCain from the United States Nuclear Regulatory Commission. He should have asked more questions. https://www.nrc.gov/docs/ML1512/ML15124A777.pdf
This is also directly connected to Uranium one as the Tenex, the receiver of the shipment is a Russian State company and part of Rosatom which bought Uranium 1.