Top Democrat on the Senate Judiciary Committee Sen. Dianne Feinstein, D-Calif., sent a letter to Chairman Chuck Grassley on Thursday in which she called for more testimony from former FBI Director James Comey, Attorney General Jeff Sessions and other individuals as part of an ongoing probe into Russian interference in the 2016 election.

Feinstein wrote to Grassley, R-Iowa, telling him there is a unanimous belief that Comey should testify before the judiciary panel in order to address unanswered questions and that she is willing to subpoena him if he is unwilling.

"If not, the Committee should take steps to compel his attendance," Feinstein wrote. "Be assured my Democratic colleagues are supportive of issuing a subpoena should it become necessary.

Feinstein also said the committee needs to hear from Sessions before the August recess.

"The Committee needs to have an opportunity to question the Attorney General about the Department's policies and priorities," Feinstein wrote. "There also remain unanswered questions about the Attorney General's prior testimony before the Committee and his role in firing Director Comey."

Both Comey and Sessions have testified before the Senate Intelligence Committee in the past two weeks.

Among other "steps" she recommended the Senate Judiciary Committee take is hearing from the individuals Comey said he had spoken to about his interactions with President Trump; those individuals include FBI Deputy Director Andrew McCabe and four other FBI officials.

"The Judiciary Committee should exercise its oversight authority and promptly arrange for the appearance of Acting FBI Director McCabe, Deputy Attorney General Rosenstein, Attorney General Sessions, and any others associated with the Department who have information relevant to this inquiry," Feinstein wrote.