Charles Cooper, the lawyer to Amb. John Bolton, says that his client will “only appear before Congress if a judge orders him to do so.”

“John Bolton was personally involved in many of the events, meetings, and conversations about which you have already received testimony, as well as many relevant meetings and conversations that have not yet been discussed in the testimonies thus far,” said Charles Cooper in the letter.

Cooper said Bolton and his former deputy, Charles Kupperman are seeking a “definitive judgment from the Judicial Branch determining their Constitutional duty in the face of conflicting demands” from the White House and Congress. The attorney — who represents both men — noted that unlike the other witnesses, Bolton and Kupperman provided direct advice to Trump regularly and would be asked during any congressional appearance to disclose sensitive foreign policy and national security information.

The House committees have also accused Bolton and Kupperman of coordinating with the White House to skirt Congressional subpoenas and delay the inquiry even further, which the two have vehemently denied.

“Dr. Kupperman stands ready, as does Ambassador Bolton, to testify if the Judiciary resolves the conflict in favor of the Legislative Branch’s position respecting such testimony,” Cooper wrote. “The House Chairs are mistaken to say Dr. Kupperman’s lawsuit is intended “to delay or otherwise obstruct the Committees’ vital investigatory work.”