The person who will decide the Democratic presidential nominee is FBI Director James Comey, Charles Krauthammer said on "Special Report" tonight.
Krauthammer explained that Bernie Sanders - despite his surging poll numbers - doesn't pose a real threat to front-runner Hillary Clinton, but the FBI investigation into her private email server does.
If Comey decides to proceed with a criminal referral of Clinton, then her campaign could collapse, Krauthammer said.
"Either it's quashed and then there's a huge scandal, or there is an indictment," Krauthammer said.
He added that in the case of an indictment, then he believes Joe Biden will step forward and offer himself as the Democratic nominee.
If there's not an indictment, then many career lawyers in the FBI will resign en masse, Krauthammer predicted.
"It will be like the Saturday Night Massacre."
Watch more from the "Special Report" panel above.