By using a private email server that potentially exposed classified information to foreign adversaries, and by taking BlackBerry devices overseas, Hillary Clinton likely committed treason, House Homeland Security Committee Chairman Michael McCaul said Thursday.

"She has had seven special access programs on these devices," the Texas Republican told Fox News' "Fox & Friends" program. "Those are the most classified, sensitive secrets in the federal government. Many of them were covert operations. She took those devices overseas against the State Department's wishes and now we find out, as [FBI Director] James Comey told me previously, that it's very likely that foreign adversary nations got into her private server."

There are security protocols to protect classified information, said McCaul, but "she exposed it to our enemies and now our adversaries have this very sensitive information that not only jeopardizes her and national security at home, but the men and women serving overseas. This is in my opinion, quite frankly, it's treason."

On Wednesday, Fox News, citing sources familiar with the FBI's investigations into Clinton's private email server, reported that there was a "99 percent accuracy" likelihood that the server was hacked by at least five foreign intelligence agents. McCaul said Clinton would "absolutely" be exposed to blackmail if she becomes president.

In addition, McCaul pointed out, President Barack Obama was communicating with Clinton, through the use of a pseudonym, on the server.

"The American people know why it was such a big deal," said McCaul. "[The server] should be in a protected environment, and it wasn't. It is vulnerable to a cyber-attack and it was. The president of the United States is communicating with her under a pseudonym. They are not stupid. They can figure that out as well. This is a huge story. It's far bigger than the accusations against Donald Trump. This goes to the heart of fitness of character to serve as commander in chief."

Fox News has also reported that Obama's senior advisor Valerie Jarrett has asked that FBI Director James Comey be dismissed, but McCaul said he does not believe she has credibility in the issue.

"James Comey, he always does what he thinks is the right thing to do," said McCaul. "He's made Republicans upset, but he's also made Democrats upset. One thing I know about him is he will do the right thing in his mind."

But in July, when Comey said he would not recommend prosecution against Clinton, McCaul said that decision was not up to the FBI. Instead, McCaul, a former Justice Department prosecutor, said the decision should have been left up to a prosecutor instead.

"That was the only criticism I had. He pretty much indicts him all the way up to not indicting her," the Texas lawmaker said.