The August rally in Charlottesville, organized by Unite the Right, which brought together several far-right groups, came amid a string of protests by white supremacist groups of removals of Confederate monuments across the South. Hundreds demonstrated against the city’s decision to remove a statue of Robert E. Lee, the Confederate general. The rally, following a torch-lit march a night earlier, devolved quickly into racial taunts, shoves and brawls. The governor declared a state of emergency, and the police and the National Guard cleared the area.

Mr. Fields was among the crowd of demonstrators “engaged in chants promoting or expressing white supremacist and other racist and anti-Semitic views,” according to the Justice Department. After they were dispersed, prosecutors said, Mr. Fields drove away and encountered a “racially and ethnically diverse crowd of individuals” at the bottom of a hill who were protesting discrimination.

“Fields slowly reversed his vehicle to the top of the hill,” prosecutors wrote in the indictment in trying to underscore his intent, “then rapidly accelerated, ran through a stop sign and across a raised pedestrian mall, and drove directly into the crowd.” Mr. Fields’s car stopped only when it hit another vehicle, and then he fled, court papers said. Ms. Heyer was killed and dozens injured.

In the hours and days afterward, Mr. Trump alternated his responses, condemning the violence but refusing at first to criticize white nationalists or the neo-Nazi slogans on display at the protest. He blamed “hatred, bigotry and violence on many sides” and said the demonstrators included “some very fine people.”

Civil rights advocates rebuked Mr. Trump, his fellow Republicans rushed to condemn the resurgence of white supremacist rallies and others aligned with the White House withdrew their support, including several corporate executives, prompting the president to disband a pair of advisory councils they served on.

But as conservatives and progressives castigated Mr. Trump, David Duke, the former leader of the Ku Klux Klan, sent the president an ominous warning. “I would recommend you take a good look in the mirror & remember it was White Americans who put you in the presidency, not radical leftists,” Mr. Duke wrote on Twitter.