However, the Democrats said that attempts by Kupperman and others not to comply with subpoenas will not delay their impeachment investigation, whether or not they go to court to try to enforce the subpoenas.
"We are not ready to admit the White House to engage us in a lengthy game in court," said Adam Schiff, secretary of the House secret service, on Monday after Kupperman had not appeared.
Schiff said he was confident that the house would eventually prevail in court, even though he did not say if the house would follow this path – assuming that a lawsuit would likely take weeks, if not months, to reach it is clarified.
"We expect the court to take up this argument shortly, but still we go further," Schiff said.
The chairmen of the three committees who conducted the house's impeachment investigation dismissed Kupperman's lawsuit. threatened him with contempt, if he did not appear. The Democrats wrote in a letter on Saturday that the lawsuit was "an obvious and desperate tactic for the President to delay and obstruct the Congress's legitimate constitutional functions and hide evidence of his conduct from the impeachment investigation."
Cooper responded with a letter On Sunday, not Kupperman denies the validity of the summons, but the president.
"If your clients' position on the matter is correct, it will prevail in court and, as I assure you, Dr. Kupperman will comply with the judgment of the Tribunal," Cooper wrote in a letter to the House of Highness Intelligence Committee.
Bolton, who was Kupperman's chief on the National Security Council, also hired Cooper as a lawyer.
Ship A Californian Democrat said on ABC's "This Week" Sunday that he expected Bolton to face similar resistance.
"We will hold public hearings and I think we will do it soon," Schiff said. "I do not want to give a precise timing because we are struggling in part with the continued efforts of the White House to obstruct our investigation and obstruct the entry of witnesses, and I suspect they will fight us if John Bolton is present; Example. "
Schiff and other Democrats have already said that witnesses and authorities who oppose and testify to documents are obstructing Congress, which could be cited in impeachment proceedings. Kupperman, however, is the first witness of the impeachment, which was threatened with the contempt of non-appearance.
Five more witnesses are scheduled to appear behind closed doors this week, including Tim Morrison, a National Security Council official repeatedly quoted in the testimony of US diplomat Bill Taylor. Three other officials who testified voluntarily were summoned to appear next week.
This story was updated on Monday with additional developments.
Zach Cohen, Suzanne Malveaux and Jake of CNN Lubbehusen contributed to this report.