The Defense Department’s top policy director submitted a letter of resignation Wednesday, saying he will leave his post at the end of the month and stating plainly that his departure was prompted by President Donald Trump.

Undersecretary of Defense for Policy John Rood assumed his role in August 2018, and will be succeeded by James Anderson, Assistant Secretary of Defense for Public Affairs Jonathan Hoffman told reporters on Wednesday.

Rood’s resignation letter, obtained by Defense Daily, makes clear that he feels his departure was forced by senior administration leaders, including the president.

“Mr. President, It’s my understanding from Secretary [Mark] Esper that you requested my resignation … therefore, as you have requested, I am providing my resignation effective February 28, 2020,” the letter says.

As the Pentagon’s chief policy leader, Rood played a key role in developing and overseeing the department’s various policies and plans. Hoffman noted in particular his role in implementing the department’s 2018 National Defense Strategy, and overseeing the development of the latest Missile Defense Review, a strategy to outline and execute the nascent U.S. Space Force, as well as emphasizing nuclear deterrence capability needs via the 2018 Nuclear Posture Review.

Earlier this month, Rood issued the Pentagon’s formal acknowledgement that the Navy had deployed the W76-2 low-yield nuclear warhead for submarine-launched ballistic-missiles.

Before taking his current post, Rood spent over 20 years in the U.S. government within the Departments of State and Defense, the National Security Council and Central Intelligence Agency, and as a staff member in the Senate. He also previously served for a decade in the private sector, including as senior vice president of Lockheed Martin International and as a vice president at Raytheon.

Upon the news Wednesday, sources and analysts questioned whether Rood’s role within the Pentagon withholding of U.S. military aid to Ukraine, which led to Trump’s impeachment by the House of Representatives, was the reason behind his forced resignation. Rood had reportedly certified that Ukraine was meeting the terms of its agreement to receive $250 million in weapons and aid.

Hoffman said considering a potential tie-in between Rood’s role in the Ukraine issue and his resignation submission would be “speculative” and that Rood’s letter “speaks for itself.”