This Will Not Pass: Trump, Biden, and the Battle for America's Future by Jonathan Martin and Alexander Burns:
Donald Trump did not attend. The departed president, then bracing for his imminent impeachment trial, left the White House on the morning of Inauguration Day, decamping to his South Florida estate hours before Biden’s swearing-in. His absence was neither surprising nor disappointing to the event organizers. Trump had announced two days after the Capitol attack, in his very last tweet before the social-media site banned his account, that he would not join the ceremonies. His early escape made him the first president since Andrew Johnson, the failed and impeached successor to Abraham Lincoln, to skip his own successor’s inauguration.