The Trump presidency featured a high volume of contentious mobilization. We describe the collection and aggregation of protest mobilization data from 2017 to 2021 and offer five observations. First, the protests were sustained at a high level throughout the Trump presidency, with the largest subset of protests positioned against Trump and the administration’s policies. Second, the grievances that drove the protests varied. Third, the National Student Walkout and the antiracism protests in 2020 had the broadest geographic spread of any reported protests in U.S. history. Fourth, the vast majority of protests did not have arrests or injuries; they were nonviolent protests. When there were arrests, most people who were arrested were committing nonviolent civil disobedience, not aggression or interpersonal violence. Fifth, in 2020, a sustained period of right-wing countermobilization began around the issues of COVID-19 lock-downs, policing and race, and Trump’s false claim about the presidential election.