The committee has already interviewed more than 150 people across government, social media and law enforcement.
President Trump says he has pardoned his former national security adviser Michael Flynn.
A federal prosecutor says an ally of President Trump was given special treatment by the Justice Department.
A federal judge on Thursday has denied a request for a new trial made by Trump ally Roger Stone following his conviction on charges related to the Russia investigation.
Democrats want briefings, documents and interviews with 15 officials as they investigate whether there was improper political interference in federal law enforcement.
Roger Stone, a staunch ally of President Donald Trump, has been sentenced to 40 months in prison on his convictions for witness tampering and lying to Congress.
Attorney General William Barr took a public swipe at President Trump, saying that the president’s tweets about Justice Department prosecutors and cases “make it impossible for me to do my job.”
Attorney General William Barr is scheduled to testify before the House Judiciary Committee late next month.
All four prosecutors have withdrawn from the Roger Stone case after the Justice Dept. announced it would reduce sentencing recommendations for Stone, a longtime confidante of Pres. Trump.
Gates will also pay a $20,000 fine and fulfill 300 hours of community service. He will be allowed to serve his jail sentence on weekends during his three years of probation.