WASHINGTON (Reuters) – President Donald Trump on Monday withdrew the nomination of Elaine McCusker to a senior Pentagon post, after reports that she had questioned the suspension of military aid to Ukraine, a key element in the inquiry leading to Trump's impeachment.

Withdrawal of McCusker's nomination to be under secretary of defense (comptroller), made in November, was announced by the White House in a statement.

The decision, following the ouster of several other officials who testified in the impeachment inquiry, was criticized by Senator Jack Reed, the top Democrat on the Senate Armed Services Committee.

“The termination of her nomination is collateral damage by a President who has vindictively purged career national security professionals caught up in the impeachment inquiry,” Reed said in a statement.

Trump was impeached by the Democratic-led House of Representatives in December. Democrats said Trump held back

$391 million in security aid to Ukraine and coveted White House meeting for President Volodymyr Zelenskiy as leverage to force Kiev into interfering in the 2020 election by smearing Democratic candidate Joe Biden.

Trump, who branded the impeachment effort a witch hunt, was acquitted last month after a trial in the U.S. Senate, where his fellow Republicans have a majority.

Following Trump's acquittal, the White House moved quickly to oust key officials whose testimony had been seen as hurting his case, including ambassador to the European Union Gordon Sondland and National Security Council staffer Lieutenant Colonel Alexander Vindman.

Reed said witness testimony and leaked emails between McCusker and the Office of Management and Budget showed that “McCusker repeatedly raised concerns about the President's unexplained hold on Ukraine security assistance and sought to ensure that the Administration was in compliance with the law.”

McCusker has been serving as deputy under secretary of defense comptroller.