Special counsel Robert Mueller is reportedly probing whether Trump confidante Roger Stone intimidated a witness who contradicted his story on his contact with WikiLeaks.
The Wall Street Journal reported the turn in the investigation based on sources in contact with Mueller's team.
The probe reportedly revolves around Stone's relationship with New York radio host Randy Credico, the man Stone claims was his "backchannel" to WikiLeaks. Credico denied Stone's claim.
Filmmaker David Lugo, an acquaintance to both men, told the Wall Street Journal that he testified before the special counsel's grand jury about a "harshly critical" blog post Stone helped him write about Credico.
Progressive activist and businessman Bill Samuels, a friend of Credico's, told the newspaper that Mueller's team questioned him about the radio host's "reaction to allegedly threatening messages" sent by Stone.
Another person familiar with Mueller's investigation said his team is looking into messages between the two men about Credico invoking the Fifth Amendment before Congress.