The aircraft gained prominence especially after the terrorist attacks on September 11, 2001. President George W. Bush was reported to have used the plane then. For later presidents, there are no confirmed indications of an actual deployment in emergencies. Typically, the plane accompanies Air Force One on foreign trips and remains on standby.
Trump is not the only head of state with such an emergency aircraft. Vladimir Putin also has the Ilyushin Il-80, also known as the "flying Kremlin." China, on the other hand, relies on a specially converted Boeing 737. The current E-4B aircraft of the U.S. are to be modernized and replaced with new models in the coming years.