House Democrats are threatening to charge a key witness in their impeachment investigation with contempt after he defied a subpoena and failed to show up at the Capitol Monday morning.

Rep. Adam Schiff Adam Bennett SchiffSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled Schiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power MORE (D-Calif.), chairman of the House Intelligence Committee, said the lawsuit filed by Charles Kupperman, a deputy to former national security adviser John Bolton John BoltonJudge appears skeptical of Bolton's defense of publishing book without White House approval Maximum pressure is keeping US troops in Iraq and Syria Woodward book trails Bolton, Mary Trump in first-week sales MORE, questioning his obligation to appear before Congress "has no basis in law" since Kupperman is now a private citizen.

ADVERTISEMENT

Schiff said Democrats will forge ahead with their impeachment investigation, vowing not to let the White House bog their investigation down in the courts.

"This is deeply regrettable. He was compelled to appear by a lawful congressional subpoena," Schiff told reporters. "Witnesses like Dr. Kupperman need to do their duty and show up."

"A private citizen cannot sue the Congress to try to avoid coming in when they're served with a lawful subpoena. And we expect that the court will make short shrift of that argument. But nonetheless we move forward."

Schiff, joined by the Democratic chairs of the House Oversight and Reform and House Foreign Affairs committees, had threatened in a letter Saturday that if Kupperman did not appear on Monday, they might hold him in contempt.

On Monday, the Intelligence chairman stopped short of saying Democrats would take that step, but left it on the table as a possible recourse.

“Dr. Kupperman had testimony we believe would corroborate the allegations of misconduct that other witnesses have made,” Schiff said. “But we move forward, and we will obviously consider — as we inform Dr. Kupperman's counsel — his failure to appear as evidence that may warrant the contempt proceeding against him.”

The Wall Street Journal has reported that Kupperman was on the July 25 phone call between President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE and Ukrainian President Volodymyr Zelensky, in which Trump pressed Zelensky to launch an anti-corruption investigation into former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, a leading candidate for the Democratic presidential nomination in 2020.

A government whistleblower has charged that Trump also threatened to withhold hundreds of millions of dollars in U.S. aid to Ukraine if Zelensky failed to comply. The episode stands at the center of the Democrats’ impeachment inquiry, launched by Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) almost five weeks ago, as investigators examine whether Trump sought to enlist a foreign power for help with his reelection.

Democrats view Kupperman as a key witness, given his proximity to the call, and suspect the White House has blocked his testimony because it might undermine Trump’s defense.

"If this witness had something to say that would be helpful to the White House, they would want him to come and testify,” Schiff said. “They plainly don't."

Republicans, meanwhile, had no qualms with the lawsuit, and they continued to trumpet claims that none of the witnesses interviewed as part of Democrats’ impeachment inquiry have implicated the president in a crime during their closed-door testimonies.

“Every time we hear from a witness, every single witness who talked to the president, each and every time they have said he has done nothing wrong,” said Rep. Mark Meadows Mark Randall MeadowsWhite House chief of staff knocks FBI director over testimony on election fraud Anxious Democrats amp up pressure for vote on COVID-19 aid Pelosi hopeful COVID-19 relief talks resume 'soon' MORE (R-N.C.), a prominent Trump ally in the House. “He is innocent of any charges.”

Meadows also said Democrats have heard from witnesses who received their information secondhand — a matter Democrats believe they would be able to rectify if they are able to hear from Trump officials like Kupperman and Bolton.

Nevertheless, Kupperman’s refusal is likely to create a hiccup for Democrats, who are seeking to draw in witnesses like Kupperman and Bolton — who are said to share the same lawyer — as they seek to get corroboration from individuals who served closely to the commander in chief.

But Democrats publicly refused to describe this as a blow, saying they will push ahead regardless.

“The investigation is overwhelmingly successful until this point. We have tremendous momentum and we are getting the information we need,” said Rep. Jamie Raskin Jamin (Jamie) Ben RaskinOVERNIGHT ENERGY: House passes sweeping clean energy bill | Pebble Mine CEO resigns over secretly recorded comments about government officials | Corporations roll out climate goals amid growing pressure to deliver On The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security House panel pulls Powell into partisan battles over pandemic MORE (D-Md.), a constitutional lawyer who serves on the House Oversight and Reform Committee.

“Let’s hope it is like a hiccup and a cup of water will make it go away.”