The Department of Defense has removed a top political appointee in charge of nuclear policy from her position, prompting concern among disarmament advocates that the Pentagon is sidelining those with less hawkish views as the Biden administration develops its official policy on nuclear weapons.

Top Pentagon officials asked Leonor Tomero, the deputy assistant secretary of defense for nuclear and missile defense, to resign from her post in recent days, according to people familiar with the matter, who spoke on the condition of anonymity to discuss a sensitive personnel matter.

The shake-up comes as the Biden administration hammers out the details of its Nuclear Posture Review, a document that each administration has released since the 1990s to set out its nuclear weapons policy and strategy, and which the administration is expected to release early next year.

The process — which Tomero had been coordinating — will clarify whether President Joe Biden plans to curtail the declared role of nuclear weapons in U.S. defense policy or roll back a $1.2 trillion, 30-year modernization of the U.S. nuclear force that progressive lawmakers want to see curbed.

One of those lawmakers, House Armed Services Committee Chairman Adam Smith, D-Wash., served as Tomero's boss in Congress for a decade before she joined the Pentagon. Tomero's departure was first reported by Politico.

Pentagon officials have characterized Tomero's departure as the product of a broader reorganization of the policymaking apparatus at the Defense Department.

"As a matter of policy, we won't comment on personnel matters," Pentagon spokesman Eric Pahon said in a statement. He said a "wide ranging team of experts" continued to work on the Biden administration's Nuclear Posture Review.

But nuclear disarmament advocates expressed concern that the Pentagon ousted Tomero from the post after just eight months in the job because her views challenge current nuclear policy that is entrenched in the building and across the military.

"People wonder why we don't learn from failures like Vietnam, Iraq and Afghanistan. The reason is simple: People who point out alternatives to current national security policies are systematically driven out of positions of authority," said Jeffrey Lewis, a professor and nuclear weapons expert at the Middlebury Institute for International Studies. "Firing her sends a clear message to everyone in the Pentagon that there is no tolerance for new ideas when it comes to our nuclear weapons policies."

Daryl Kimball, executive director of the Arms Control Association, said in a tweet that Tomero's firing was not the first time the Department of Defense "deep state has 'reorganized' a smart, competent person who poses commonsense (questions) that challenge the nuclear status quo out of office."

A Pentagon official, speaking on the condition of anonymity to discuss a personnel matter, denied that Tomero's views played any role in her departure from the post.

"This was a reorganization decision to more appropriately align our organization with policy objectives," the official said. "This was not a difference in opinion or policy."

Tomero did not respond to a request for comment.

The personnel shake-up comes as the Biden administration faces critical choices on its nuclear policy in the coming months.

President Barack Obama considered declaring a "No First Use" policy in his final days, meaning the United States would pledge to use nuclear weapons only if it was hit first by a nuclear strike. Obama, however, ultimately stood down after facing opposition to the move within his cabinet.

But Biden has suggested he may favor such a declaration.

In a January 2017 speech, Biden said it was "hard to envision a plausible scenario in which the first use of nuclear weapons by the United States would be necessary or make sense."

Biden also said he believed deterring or retaliating against a nuclear attack should be the "sole purpose" of the U.S. nuclear arsenal. The Obama administration stopped short of adopting that belief as policy, and the Trump administration explicitly rejected it in its 2018 nuclear posture review.

Biden is also facing pressure from progressive lawmakers to curtail a vast modernization of the U.S. nuclear force that Obama agreed to undertake a decade ago in exchange for the GOP-controlled Senate's ratification of the New START Treaty.

In a letter to Biden last month, Smith, Tomero's former boss when she served on the House Armed Services Committee's professional staff, urged the president to consider a "No First Use" policy for U.S. nuclear weapons and to "take a hard look" at whether all aspects of the nuclear modernization currently underway are necessary.