The correspondence is part of what led GAO to accuse the Trump administration of blocking its inquiry and conclude last week that Trump's decision to withhold military aid violated federal law. Democrats have cited that decision as they press their case that Trump should be removed from office for pressuring Ukraine's president to investigate Democrats, including 2020 rival Joe Biden. Democrats allege that Trump used the hold on military aid to raise pressure on Ukraine.

"Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law," GAO's report concluded.

The documents released by Van Hollen (D-Md.) indicate that GAO had asked the White House budget office for details on how the hold on military aid complied with the Impoundment Control Act, the law the GAO argues Trump violated.

The documents also included a response to the inquiry from the Pentagon, which suggested it couldn't respond to GAO's inquiry without first engaging in "coordination with the other agencies involved."

Van Hollen ripped the Trump administration for refusing to cooperate with GAO.

"The White House refused to respond altogether and blocked DOD from providing an independent response as well," he said in a statement. "This is another example of the Administration's continued attempts to cover up their wrongdoing and unlawful actions."