evidence: President Trump has undercut the effectiveness of a basic public health measure — mask-wearing — by refusing to wear a mask and mocking people for wearing them. He has also suggested that people wear masks not for any health benefits but to signal disapproval of his administration. During public appearances, he has falsely claimed that the Centers for Disease Control and Prevention (CDC) found that 85 percent of mask-wearers eventually contract the coronavirus, despite the fact that the study referenced did not even investigate this question. On occasion the president has refused to wear a mask (implicitly encouraging others to do the same) in places where state governments require people to wear masks to protect public health. Other Trump administration officials, including Vice President Mike Pence, have also not worn masks in places where masks are required. Pence also promoted a Trump campaign event where attendees did not adhere to state guidelines on masks. In October 2020, an adviser to President Trump stated without evidence that masks do not help contain the spread of Covid-19 in a post that Twitter later blocked for violating its policy against sharing virus-related misinformation. This behavior has contributed to mask-wearing being a uniquely political issue in the United States. Many in Congress and among the general public often refuse to wear masks, notwithstanding research showing that wearing face masks reduces the spread of the coronavirus.