House lawmakers spearheading the impeachment inquiry of President Donald Trump issued subpoenas for the Department of Defence and the White House budget office on Monday, demanding documents related to US relations with Ukraine.
Democrats in the House of Representative have already issued subpoenas for the White House, Vice President Mike Pence and the State Department, including Secretary of State Mike Pompeo.
The lawmakers have warned that failure to comply may be seen as obstruction and held against any officials in the executive branch.
The Democrats said in a letter to Secretary of Defence Mark Esper that their investigation is focusing on whether Mr Trump endangered U.S. national security by seeking foreign interference in the upcoming U.S. elections and withholding military aid to Ukraine.
In July, Trump held a phone call with Ukrainian President Volodymyr Zelensky and asked for a “favour” in investigating Joe Biden, currently the Democrats’ leading candidate for the party’s nomination to run against Mr Trump next year.
The president has said there was no quid pro quo, but text messages between U.S. diplomats released last week show at least one was alarmed that Mr Trump was seeking help from Ukraine with his domestic political campaign at the expense of U.S. foreign policy objectives.