It will be the most senior position affected so far by Republican Senator Tommy Tuberville's move to stall Defense Department nominations, which he says he will continue to do until the Pentagon reverses course on assisting troops who travel to receive abortions.

Tuberville insists the policy is illegal, while Defense Secretary Lloyd Austin has said it is legally sound and that delaying the approval of the nominees "harms America's national security and hinders the Pentagon's normal operations."

Though the Senate -- which must sign off on nominations of military officers -- can still vote on them individually, Tuberville's "hold" means they cannot be quickly approved in groups by unanimous consent, and his office says that more than 200 are currently affected.

General David Berger's term as Marine Corps commandant "will expire on 10 July 2023, at which time he must vacate the office, regardless of whether a successor has been appointed," spokesman Major Jim Stenger said.

The assistant commandant, General Eric Smith -- whom the White House has nominated to replace Berger -- will serve in an acting capacity "until a new commandant is confirmed by the Senate and appointed to the position," Stenger added.

Colin Smith, a senior researcher at RAND, said Smith "will essentially have to do double duty," performing both his current job as well as serving as acting commandant, "which is equally if not more demanding."

- 'Limited by law' -

The US Supreme Court in June 2022 struck down the nationwide right to abortion, meaning troops stationed in places that subsequently banned the procedure must now take leave and travel to areas where it is legal to obtain one.

In response, Austin directed the Defense Department to develop policies -- which were released in February -- to allow service members to take administrative absences in order to receive "non-covered reproductive health care," and to establish travel and transportation allowances to help them cover costs.

Tuberville, a member of the Senate Armed Services Committee, tweeted in mid-February that because Austin is "following through with his radical plan to facilitate thousands of abortions a year with taxpayer dollars," he would "hold all DoD civilian & general/flag officer nominees that come before the US Senate."

He has said the hold "has no effect on readiness," and that he will keep it in place "until the Pentagon follows the law (or) Congress changes the law."

Other top officers are also due to leave office in the coming months, including Chief of Staff of the Army General James McConville, Chief of Naval Operations Admiral Mike Gilday and Chairman of the Joint Chiefs of Staff General Mark Milley.

"The tenure of service chiefs is limited by law, and thus, incumbents must vacate their positions at the appointed time and may only be extended under extraordinary circumstances," Austin wrote in an early May letter to Senator Elizabeth Warren.

"Without these leaders in place, the US military will incur an unnecessary and unprecedented degree of risk at a moment when our adversaries may seek to test our resolve," he said.