Sen. Tom Carper, D-Delaware, joined Sen. Richard Blumenthal, D-Connecticut, and a group of senators in calling on Attorney General Jeff Sessions to appoint an independent special counsel to investigate possible illegal communications between retired Lt. Gen. Michael Flynn and representatives of the Russian government, as well as efforts by Flynn and other White House officials to conceal any wrongdoing.

“An independent investigation is now necessary to determine what Gen. Flynn did, who knew about it, and when,” the Senators wrote. “To maintain the confidence, credibility and impartiality of the Department of Justice, we urge you to immediately appoint an independent special counsel to investigate collusion with the Russian government by Gen. Flynn and other Trump campaign, transition and administrative officials.”

In addition to Carper and Blumenthal, the letter was signed by U.S. Sens. Tom Udall, D-New Mexico; Tammy Baldwin, D-Wisconsin; Edward J. Markey, D-Massachusetts; Jeff Merkley, D-Oregon; Sherrod Brown, D-Ohio; Dick Durbin, D-Illinois; Chris Van Hollen, D-Maryland; Cory A. Booker, D-New Jersey; and Patrick Leahy, D-Vermont.