President Donald Trump has lost the support of many former loyalists in his administration after a riot at the US Capitol that he helped provoke, and his White House is in “meltdown” as it lurches through his final days, current and former officials said.

While Democrats plan to introduce an article of impeachment against Trump on Monday, many White House staff members are upset and embarrassed by the turn of events and are eager to move on. They said they have faced criticism from peers and are worried about damage to their reputations and job prospects...