The House is investigating whether President Trump lied in his written answers to special counsel Robert Mueller in the wake of new revelations from Roger Stone's trial, CNN reports.

Why it matters: House Democrats had previously suggested in a court filing in September that Trump may have lied, but they drew "new focus" to the allegations during opening arguments Monday in a case involving the Judiciary Committee's request to unseal grand jury materials from the Mueller report, per CNN.

Former Trump deputy campaign chairman Rick Gates testified in last week's trial that Roger Stone spoke with then-candidate Trump in a July 2016 phone call.

A minute after ending the call, Trump told Gates, in reference to WikiLeaks, that "more information would be coming."

Trump told Mueller in written answers included in the special counsel's report that he did not recall discussing WikiLeaks with Stone.

The big picture: According to the Washington Post, House general counsel Douglas Letter told the D.C. Circuit Court of Appeals Monday that the grand jury materials are necessary for the ongoing impeachment inquiry.

“Did the president lie? Was the president not truthful in his responses to the Mueller investigation? The House is trying to determine whether the current president should remain in office. This is unbelievably serious and it’s happening right now, very fast.”

— Douglas Letter

Go deeper: Six Trump associates convicted in Mueller-related investigations