Sen. Cory Booker (D-N.J.), a Hillary ClintonHillary Diane Rodham ClintonMore than 200,000 Wisconsin voters will be removed from the rolls Trump is threatening to boycott the debates — here's how to make sure he shows up Trey Gowdy returns to Fox News as contributor MORE supporter, said Sunday it's not possible that the presumptive Democratic presidential nominee will be indicted in the FBI's investigation into her use of a personal email server while secretary of State. 

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"That's just not going to happen," Booker said on CNN's "State of the Union." 

The FBI interviewed Clinton Saturday for three and a half hours as part of the ongoing investigation. 

Booker called the interview routine and said he expects the investigation to wrap up soon, noting that Clinton has been open for an interview since last summer.

"I think this is something that's just routine, and I think we will see the investigation closing up," he said. 

Booker would not directly answer a question about whether he is being vetted by the Clinton campaign as a possible running mate.

"I'm referring questions ... to the woman that's going to have to make this decision," Booker said. 

"That's not a no?" asked host Brianna Keilar. 

"That is exactly what it is. If you have a question like that, please direct it to the Clinton campaign," Booker said.