A former U.S. attorney thinks Hillary Clinton could face a criminal indictment from the FBI within the next 60 days.

Joe DiGenova, a Republican U.S. attorney appointed by President Reagan, said Clinton's "biggest problem right now" is the open FBI investigation into the contents of her private emails.

"They have reached a critical mass in their investigation of the secretary and all of her senior staff," DiGenova said Tuesday on the "Laura Ingraham Show" radio program. "And, it's going to come to a head, I would suggest, in the next 60 days."

FBI Director James Comey has refused to answer questions about when his agents will wrap up a months-long probe into whether Clinton and her staff mishandled classified information on an unsecured network.

Clinton's campaign has maintained that the investigation is not focused on Clinton herself and is not criminal in nature.

"It's going to be a very complex matter for the Department of Justice, but they're not going to be able to walk away from it," DiGenova said. "They are now at over 1,200 classified emails. And, that's just for the ones we know about from the State Department. That does not include the ones that the FBI is, in fact, recovering from her hard drives."

The former U.S. attorney noted Clinton has yet to be interviewed by the FBI, a step he said will likely occur before agents make their findings public.

But DiGenova warned the decision to charge Clinton personally with a crime lies with Attorney General Loretta Lynch, putting the Obama administration in a difficult political position.

"I believe that the evidence that the FBI is compiling will be so compelling that, unless [Lynch] agrees to the charges, there will be a massive revolt inside the FBI, which she will not be able to survive as an attorney general. It will be like Watergate. It will be unbelievable," DiGenova said.

"The evidence against the Clinton staff and the secretary is so overwhelming at this point that if, in fact, she chooses not to charge Hillary, they will never be able to charge another federal employee with the negligent handling of classified information," he added. "The intelligence community will not stand for that. They will fight for indictment and they are already in the process of gearing themselves to basically revolt if she refuses to bring charges."