As Special Counsel Robert Mueller continues his investigation into Russian involvement in the 2016 U.S. presidential election, the obvious question is, what's next? 

Mueller's investigation has resulted thus far in indictments of two Trump campaign advisors, a national security advisor, a national foreign policy advisor, 13 Russian nationals, and three Russian companies. Charges range from conspiracy and money laundering to identity theft.

WGBH senior reporter Phillip Martin joined journalist Garrett Graff at the Harvard Kennedy School’s Shorenstein Center to break down the complex probes of the Mueller investigation, the effects of previous indictments, and the next steps in the investigation.

Watch Forum Network's talk with Garrett Graff at the Shorenstein Center
Garrett Graff speaks with fellows at the Shorenstein Center in Cambridge, Mass.
Forum Network

“I think one of the most important things to understand is knowing what we know that Bob Mueller hasn’t told us yet,” said Graff. “There are at least two very major pieces of evidence in this investigation that we know about that haven’t been made public.”

Graff authored the 2011 book "The Threat Matrix: Inside Robert Mueller’s FBI and the War on Global Terror." He is currently the director of The Aspen Institute Cybersecurity & Technology Program, and he has served as the editor of "The Washingtonian" and "POLITICO."

» MORE: Listen to Graff's lunchtime talk with fellows of the Shorenstein Center, recorded by WGBH Forum Network.