Mark Vandroff, the senior director for defense policy at the National Security Council and a retired Navy captain, did not cite a reason for his departure in a letter sent to national security adviser Robert O’Brien and obtained by Defense News.

Vandroff’s resignation follows the resignation of deputy national security adviser Matthew Pottinger on Wednesday. Media outlets have reported that several top national security aides are also considering resigning.

Vandroff declined to comment on his resignation. The White House did not respond to a Thursday afternoon request for comment on any resignations in the wake of yesterday’s violent confrontation at the Capitol between a pro-Trump mob and police.

In his year in office, Vandroff worked on the Abraham Accords, an agreement brokered between the United Arab Emirates, Bahrain and Israel that extended official recognition of the state of Israel. A former major program manager for the Arleigh Burke-class destroyer program, Vandroff was also instrumental in shaping the administration’s push to kick off a major buildup of the fleet as part of a naval arms race with China.

In a letter, Vandroff thanked O’Brien for the opportunity to serve on the National Security Council.

“In the last year is has been a great pleasure to work for you on the staff of the NSC to implement the President’s policies and work to make America and the world safer and more secure,” Vandroff wrote. “I was privileged to work alongside the most talented, dedicated, and patriotic group of colleagues a person could imagine, here at the NSC, within the broader EOP [Executive Office of the President] and across the inter-agency in the Departments of Defense and State, and the Intelligence Community. I will always be grateful to you for the opportunity you provided me to serve our great nation.”

Joe Gould in Washington contributed to this report.

.

.