Congressional investigators have obtained nearly 40,000 pages of subpoenaed bank records and dozens of hours of testimony from key witnesses, including several high-ranking Justice Department officials currently tasked with investigating the president's son, Hunter Biden.
A shutdown affects nearly every corner of the US government, from the delivery of welfare cheques and publishing of national economic data to the operation of federal courts, museums and national parks.
Democrats, who decry the investigation as a political ploy aimed at hurting Biden and helping Donald Trump as he runs again for president, planned to bring Michael Gerhardt, a law professor who has appeared as an expert in two previous impeachment efforts.