Franken said Pence, who ran the Trump transition, was responsible for some of Trump's worst Cabinet choices, including Environmental Protec tion Agency head Scott Pruitt, Education Secretary Betsy DeVos, Health and Human Services Secretary Tom Price, and Office of Management and Budget Director Mick Mulvaney.
On the other hand, Franken said, a Pence presidency might be better than Trump on foreign policy.
"If you're talking about how we handle North Korea or something like that, I'd probably be more comfortable with Pence ultimately making those decisions than Trump, because of Trump's personality and character," Franken said.
Franken, now in his second term, said he was concerned by Trump's behavior because it's "so outside the norm," and said he worried that impeachment could make the president even worse.
"I don't know what he will do if he looks like he's going to be impeached and he wants to deflect," Franken said. "I don't know what he's capable of, and that really does concern me."