Former national security adviser Mike Waltz defended his use of the messaging app Signal during a confirmation hearing Tuesday during which lawmakers largely avoided the topic.

Sen. Cory Booker, D-NJ, criticized Waltz’s inability to take accountability. Booker said Waltz “denied” and “deflected” rather than own up to his mistakes, something the New Jersey senator said is a “failure of leadership.” He called Waltz’s actions a show of “profound cowardice.”

Waltz is a former Green Beret and Florida representative who resigned from Congress to join the Trump administration. He served as national security adviser for roughly three months. Trump reshuffled his team and named Secretary of State Marco Rubio acting national security adviser on May 1.