The political rise of Donald Trump and the ideology of Trumpism has had a major impact on American politics, culture, and its response to the COVID-19 pandemic. We began the process of validating a psychometric model of Trumpism using three waves (~1000 participants per wave) of data from national online surveys of adults conducted in the United States from June 2020 to February 2021 as part of the COVID-19 Adjustment and Behaviors Survey. We found that the covariance among measures of Trump approval and attitudes about race, immigration, policing, guns, and media bias were best accounted for by a single Trumpism factor, and that this factor was strongly related to attitudes about a rigged 2020 Presidential election, the Insurrection of January 6, 2021, and Trump idolatry. Trumpism was also associated with Republican party affiliation and White race, but had only small associations with age, sex, income, and education. Trumpism was associated with increased odds of a positive COVID-19 diagnosis, skepticism about the seriousness of COVID-19, lack of support for government restrictions to reduce the spread of COVID-19, less adherence to social distancing and mask wearing guidelines, anti-vax attitudes, and hesitancy to receive a COVID-19 vaccine. Results indicate these measures provide a valid assessment of Trumpism which is likely to continue to play a major role in American political and cultural life for the foreseeable future.