Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) on Thursday said the White House had blocked its cyber czar from testifying before the Senate Armed Services Committee on U.S. efforts to defend the nation against cyberattacks, and later signaled that the official could be subpoenaed to appear before the committee.

Rob Joyce, a member of the National Security Council (NSC), was invited to testify before the full committee Thursday morning. However, McCain, the panel chairman, said in his opening remarks that the White House had declined to have him testify, citing executive privilege and “precedent against having nonconfirmed NSC staff testifying before Congress.”

While such a move has been consistent with past practices by both Republican and Democratic administrations, McCain asserted that the issue of cybersecurity “requires us to completely rethink our old ways of doing business.”

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“I would also like to note at the outset the empty chair at the witness table,” McCain said during opening remarks. “Unfortunately, but not surprisingly, the White House declined to have its cyber coordinator testify.”

He said Joyce’s absence underscored the “fundamental misalignment between authority and accountability in our government today when it comes to cyber.”

“All of our witnesses answer to the Congress for their part of the cyber mission. But none of them is accountable for addressing cyber in its entirety. In theory, that is the White House Cyber Coordinator’s job, but that nonconfirmable position lacks the full authority to make cyber policy and strategy and direct our government’s efforts,” McCain said. “ And that official is literally prohibited by legal precedent from appearing before the Congress.”

Later, McCain signaled that Joyce could be subpoenaed, in response to a suggestion from Sen. Bill Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE (D-Fla.). “I think that has to be discussed," McCain said.

McCain told reporters after the hearing that the committee would meet and consider whether or not to subpoena Joyce.

“We’re going to have a meeting of the committee and discuss the issue," he said.

Thursday’s hearing featured testimony from several top cybersecurity officials from across different federal departments, including Kenneth Rapuano, the Pentagon’s assistant Defense secretary for homeland defense and global security; Scott Smith, the assistant director for the FBI’s cyber division; and Christopher Krebs, the acting undersecretary for the Department of Homeland Security entity charged with protecting federal civilian networks and critical infrastructure from cyber threats.

Joyce, the former leader of an elite hacking group at the National Security Agency, was brought into Trump’s White House in the early months of the new administration.

This post was updated at 12:21 p.m.