House Homeland Security Committee Chairman Michael McCaul, R-Texas, said Thursday that Hillary Clinton's decision to keep a private email system when she led the State Department amounts to "treason."

McCaul made that charge because he said he's been told that Clinton's emails were likely hacked by foreign adversaries, which could have given away critical information.

McCaul said on Fox News that FBI Director James Comey told him "it's very likely that foreign adversary nations got into her private server. This is why you have security protocols, to protect classified information."

"This is, in my opinion, quite frankly, it's treason."