President Trump returned on Monday to his post-impeachment score-settling, withdrawing the nomination of Elaine McCusker to a top Defense Department post. Ms. McCusker had questioned the suspension of assistance to Ukraine, a central line of inquiry in the president’s impeachment…

The president’s anger at her stems from email exchanges in August in which Ms. McCusker, then a deputy under secretary of defense overseeing spending, questioned Mr. Trump’s freeze on military aid for Ukraine…

A political appointee at the budget office, Michael P. Duffey, wrote a lengthy email to Ms. McCusker, with whom he had been at odds throughout the summer, about how long the administration could withhold military aid to Ukraine.

Mr. Duffey tried to shift blame for the delay in the funding from the White House to the Pentagon.

Forty-three minutes later, Ms. McCusker replied:

“You can’t be serious,” she wrote. “I am speechless.”