Deputy national security adviser Nadia Schadlow resigns

Schadlow is the third senior national security official to resign or be pushed out in the wake of national security adviser John Bolton's entrée to the White House. She submitted her resignation on Tuesday, according to a copy of her resignation letter obtained by CNN, and a senior White House official said she will remain in her role until April 27 to assist with the transition.

"The administration thanks Dr. Schadlow for her service and leadership in crafting the President's 'America First' national security strategy. The strategy has set a strong foundation going forward for protecting the homeland, promoting American prosperity, preserving peace through strength and advancing American influence. We wish Nadia and her family the best," White House spokesman Raj Shah said in a statement to CNN.

Sources close to the National Security Council have for weeks expected that Schadlow, who was a close adviser to Lt. Gen. H.R. McMaster, would resign or be pushed out after President Donald Trump announced he was replacing McMaster with Bolton. A senior White House official said Schadlow spoke with Bolton on Tuesday and submitted her resignation "to allow him to build his own NSC leadership team." Schadlow offered to remain on board for several weeks to ensure a smooth hand off, the official said.

Bolton has yet to announce any new senior staff who will join him at the National Security Council, though a White House official said Bolton has begun assembling a team.

Schadlow was a principal author of the President's National Security Strategy document, which sought to outline the administration's foreign policy goals and view of the world. She rose to the position of deputy national security adviser for strategy in January following the departure of her predecessor, Dina Powell.

In a resignation letter to the President, Schadlow thanked Trump for "the opportunity to serve you and the American people" and said she was "proud to work with LTG H.R. McMaster and the National Security Council team."

"Together, we captured your vision for a strong and confident American and developed your America First National Security Strategy -- which turned that vision into a strategic direction for your administration," Schadlow wrote. "And I am particularly proud that you were able to submit your NSS to Congress earlier than any previous administration...on time and under budget!"

Her resignation is likely to evoke some concern in foreign policy circles in Washington, where Schadlow has been viewed as one of the rare, reliable steady hands guiding foreign policy in the Trump White House.

News of her resignation comes a day after the White House's homeland security adviser Tom Bossert was unexpectedly pushed out on Tuesday, a move driven by Bolton's desire to put his own team in place. The NSC's chief spokesperson Michael Anton also resigned under pressure on Sunday evening, after learning he would be fired.

Schadlow's departure is not expected to be the last as Bolton puts his imprint on the National Security Council.

Bolton has begun reviewing the resumes of top staffers currently serving on the National Security Council, a source close to the NSC told CNN. The NSC's human resources department has also asked all staff at the director level to submit their resumes if they are not already on file as part of the review process, the source said.