WASHINGTON — Defense Secretary Mark Esper will not comply with a subpoena from House Democrats related to their impeachment inquiry, according to a letter sent Tuesday to Democratic leadership from the Department of Defense.

In the letter to the chairmen of the House Intelligence, Foreign Affairs and Oversight committees, the Pentagon cites a “number of legal and practical concerns” as their reason for not complying. They include the House not officially voting to authorize an impeachment inquiry and that some of the information the House is requesting “appears to consist of confidential Executive Branch communications that are potentially protected by executive privilege.”

This is a shift from just days ago when Esper indicated he was willing to work with Democrats on the inquiry.

Democrats are investigating whether President Donald Trump improperly withheld military aid for Ukraine as leverage to compel Ukrainian President Volodymyr Zelenskiy to investigate former vice president Joe Biden, a potential rival of Trump’s in the 2020 election.

House Democrats are seeking information and documents from Esper relating to the decision from the White House to withhold the authorized military aid.

House Democrats sent a subpoena to Esper on Oct. 7, giving him until Tuesday to comply. The House has warned that failure to do so would be evidence of obstruction of justice.

In the letter sent Tuesday, the Department of Defense pushed back on the notion that failure to comply would constitute obstruction of justice. “Invoking reasonable legal defense to a subpoena, including invoking legal privileges that are held by the President, in no way manifests evidence of obstruction of otherwise warrants an adverse inference,” the letter reads.

The White House has vowed not to comply with the impeachment inquiry and other officials such as Vice President Mike Pence and Secretary of State Mike Pompeo have failed to meet requests for documents.