The US government has experienced multiple shutdowns in the past, with some lasting only a few days and others extending into weeks. A shutdown typically occurs when Congress fails to pass budget legislation on time, causing federal agencies to cease non-essential functions until new funding is enacted. Since 1981, there have been four "true" shutdowns, including the longest-lasting one in December 2018 and January 2019, which lasted for 35 days. A shutdown can be considered complete if at least some portions of the federal government cease operations or result in a furlough for federal employees before January 1, 2024. The resolution criteria for this event is based on reports from credible sources indicating that a shutdown has occurred, rather than just a brief lapse in funding.