But Mr. Dorsey was not sold on a permanent ban of Mr. Trump. He emailed employees the next day, saying it was important for the company to remain consistent with its policies, including letting a user return after a suspension.

Many workers, fearing that history would not look kindly upon them, were dissatisfied. Several invoked IBM’s collaboration with the Nazis, said current and former Twitter employees, and started a petition to immediately remove Mr. Trump’s account…

By the next morning, though, Mr. Trump was back at it. He tweeted that his base would have a “GIANT VOICE” and that he would not attend the Jan. 20 inauguration.

Twitter’s safety team immediately saw Trump fans, who had been saying the president abandoned them, post about further unrest, said the people with knowledge of the matter. In a Parler message that the safety team reviewed, one user said anyone who opposed “American Patriots” like himself should leave Washington or risk physical harm during the inauguration.