Democrats on the House Judiciary Committee on Thursday demanded that acting Attorney General Matthew Whitaker take immediate steps to protect special counsel Robert Mueller’s ongoing investigation into President Trump’s alleged ties to Russia, after what they called Trump’s “forced firing” of former Attorney General Jeff Sessions.

“The forced firing of Attorney General Sessions appears to be part of an ongoing pattern of behavior by the president seeking to undermine investigation into Russian interference in the 2016 presidential election,” wrote Rep. Jerry Nadler, D-N.Y., and other committee Democrats in a Thursday letter to both Whitaker and committee Chairman Bob Goodlatte, R-Va.