US President election in 2016 (Photo: Thanh Tuan/VNA)

Chairman Richard M. Burr told a news conference with Senator Mark Warner that the issue of collusion is still open. Burr said the Senate panel hoped to complete its inquiry and issue findings by the end of December. The probe has expanded into new areas, including Russia’s clandestine use of Facebook, Twitter and other social media, leaving the timetable uncertain. Senate investigators have interviewed more than 150 witnesses, including some Trump family members and campaign aides. They also have reviewed 100,000 pages of documents, including emails, phone records, campaign papers and intelligence reports.