A Republican former U.S. attorney believes Democratic presidential front-runner Hillary Clinton could be facing imminent indictment over her email scandal, possibly roiling the Iowa caucuses or the New Hampshire primary in February.

Joe DiGenova, a one-time federal prosecutor originally appointed by President Reagan, told conservative radio host Laura Ingraham Tuesday that the FBI's still-pending investigation of Clinton's email server seems to have reached 'a critical mass.'

Congressional Republicans last spring discovered that Clinton used a private, home-based email server in her New York home while she was secretary of state from 2009 to 2013. The scandal has dogged her presidential campaign for almost the entire past year.

The FBI has been probing whether any classified intelligence was compromised through Clinton's unusual email setup, but she has steadfastly denied any wrongdoing and has yet to be charged with any crime.

DiGenova said that may be about to change.

Scroll down for video

Former secretary of state Hillary Clinton has been dogged for almost an entire year by controversies stemming from her use of a private, home-based email server while she was heading the State Department between 2009 and 2013

Joe DiGenova, a former U.S. attorney originally appointed by President Ronald Reagan, believes Hillary Clinton is facing imminent indictment over the mishandling of classified intelligence

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

FBI Director James Comey has resisted efforts to lay out a timeline for his agency's probe of the Clinton case, but if it is as imminent as DiGenova believes, it could devastate Clinton's campaign. The Iowa caucuses are on Feb. 1 and the New Hampshire primary is on Feb. 9.

'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.'

One telling event would be a personal interview between Clinton and the FBI. Although the former secretary of state famously testified at an 11-hour congressional hearing in October, she has not yet been interviewed by federal agents.

DiGenova said such an interview would likely precede any public release of the agency's conclusions in the case.

Clinton campaigning in Sioux City, Iowa, on Tuesday

DiGenova on 'Meet the Press' in 1998 discussing the Monica Lewinsky case

A recommendation for prosecution would not only roil the presidential race, but would put President Barack Obama in an unbelievably difficult position. Decisions about prosecution, DiGenova noted, do not lie with the FBI but with the Justice Department - headed by Attorney General Loretta Lynch.

'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,' he 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,' DiGenova continued.

'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.'