(CNN) The House Judiciary Committee gaveled in Tuesday to an empty witness chair for the second time this month after former White House counsel Don McGahn did not appear after he was subpoenaed .

The first witness who did not show for his scheduled hearing, Attorney General William Barr, was later voted by the committee to be held in contempt over not giving Congress the undredacted Mueller report. Now McGahn appears poised to be the next in line for a contempt vote before the committee.

"Our subpoenas are not optional," Nadler said at Tuesday's hearing. "Mr. McGahn has a legal obligation to be here for his scheduled appearance. If he does not immediately correct his mistake, this committee will have no choice but to enforce the subpoena against him."

Nadler told CNN's Chris Cuomo on Monday evening that if McGahn didn't appear , "the first thing we're going to have to do is hold McGahn in contempt."

Nadler said Tuesday that he was prepare to go to court to obtain McGahn's testimony.

McGahn's attorney William Burck told the committee on Monday that McGahn would not appear after the White House directed him not to testify, arguing he is immune from having to appear before Congress over his role as an adviser to the President.

"Under these circumstances, and also conscious of the duties he, as an attorney, owes to his former client, Mr. McGahn must decline to appear at the hearing tomorrow," Burck wrote.

In instructing McGahn not to testify before the House Judiciary Committee, the White House cited a Justice Department opinion that says the President's personal aides cannot be compelled to testify about their official work and have "absolute immunity" from congressional subpoenas.

Ultimately, the decision was made because the White House believed invoking immunity was the most straightforward argument to shield McGahn from testifying and create a scenario that would likely play out in the courts, which could take years to resolve and is a timeline that works in the administration's favor.

The decision about invoking immunity for McGahn was one the White House counsel's office was leaning on, but struggling with for the last several weeks, according to sources who are familiar with the internal discussions but not authorized to speak publicly.

Officials in the counsel's office zeroed in on what played out when former President George W. Bush's former top counsel, Harriet Miers, and his former chief of staff, Joshua Bolten, refused to comply with subpoenas issued by the House Judiciary Committee. A judge later ruled in 2008 that they couldn't ignore them.

The White House has raised concerns that McGahn's case could follow a path similar to what happened to Miers.

At one point, there was talk internally of having McGahn answer lawmakers' questions behind closed doors, where it would be easier to have discussions about what is privileged and what isn't, compared to a public testimony in front of the cameras.

Democrats want to hear from McGahn because he was a key witness in special counsel Robert Mueller's investigation into obstruction of justice. Nadler outlined McGahn's role in the report in his opening statement, arguing Tuesday that Trump would have been charged with obstruction if he was not President.

"I believe that each of these incidents, documented in detail in the Mueller report, constitutes a crime," Nadler said. "But for the Department of Justice's policy of refusing to indict a sitting President, I believe he would have been charged with these crimes."

McGahn's absence is the latest instance in which the Trump administration has stonewalled congressional Democrats' investigations into the President, a blockade that has prompted some Democrats to argue it's time to open an impeachment inquiry.

When Barr didn't appear earlier this month over a dispute about whether staff attorneys could question him, Democrats played up the theatrics, with Rep. Steve Cohen of Tennessee bringing a bucket of Kentucky Fried Chicken and a ceramic chicken.

There was no chicken at Tuesday's proceedings. But that didn't stop Republicans from charging that Democrats were engaging in political theatrics.

"Here we go again — the theater is open," said Georgia Rep. Doug Collins, the top Republican on the committee. "Even gaveling in today's hearing without a witness is theatrical. ... I just am glad to see today that we don't have chicken on the dais."

Collins argued that Nadler "rushed to maximize headlines" by issuing a subpoena instead of trying to bring in McGahn to testify voluntarily.