"I'm not going to comment on what he may or may not have done for the United States government, but in the emails that were on Hillary Clinton's private server, there were conversations among her senior advisors about this gentleman," he said on "Face the Nation." Cotton was speaking about Shahram Amiri, who gave information to the U.S. about Iran's nuclear program.

The senator said this lapse proves she is not capable of keeping the country safe.

"That goes to show just how reckless and careless her decision was to put that kind of highly classified information on a private server. And I think her judgment is not suited to keep this country safe," he said.