They convened to craft a plan for answering the onslaught on American democracy, and they soon reached a few key decisions. They would stay off the streets for the moment and hold back from mass demonstrations that could be exposed to an armed mob goaded on by President Donald J. Trump.

They would use careful language. In a presentation, Anat Shenker-Osorio, a liberal messaging guru, urged against calling the attack a “coup,” warning that the word could make Mr. Trump sound far stronger than he was — or even imply that a pro-Trump militia had seized power.

And they would demand stern punishment for Mr. Trump and his party: Republicans at every level of government who incited the mob “must be removed or resign,” read one version of the group’s intended message, contained in Ms. Shenker-Osorio’s presentation and reviewed by The New York Times…

By the time rioters ransacked the Capitol, the machinery of the left had already been primed to respond — prepared by months spent sketching out doomsday scenarios and mapping out responses, by countless hours of training exercises and reams of opinion research.