The questions about Stone's past reveal how prosecutors are trying to establish a pattern of whether Stone has toed -- or even crossed -- the line in his prior political work. The lines of inquiry also raise the possibility that investigators could be readying charges against Stone for crimes unrelated to the Russian hacking.

"Roger has carefully crafted his public image and sometimes that, I think, doesn't work in his favor," said Kristin Davis, a Stone friend who has worked on and off with him for 10 years and recently testified before the grand jury. "He's a victim of his own reputation."

Stone, who says he hasn't been contacted by Mueller's team, has been blunt about the prospect of facing charges. 

"It is entirely likely that Mueller is squeezing some of my current or former associates to tell lies about me," Stone said in an interview with The Influential newsletter. "By the same token, Mueller may seek to bring some bogus charge against me to induce me to testify against the President. I am not saying I have any negative information against the President - I'm saying I won't be pressured into making s--- up. This I will not do."