People wearing face masks visit the National Mall in Washington, D.C., the United States, July 11, 2020. The number of COVID-19 cases in the United States reached 3,225,721 as of 3:34 p.m. local time on Saturday, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)

People wearing face masks visit the National Gallery of Art Sculpture Garden in Washington, D.C., the United States, July 11, 2020. The number of COVID-19 cases in the United States reached 3,225,721 as of 3:34 p.m. local time on Saturday, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)

A woman rides a scooter on the National Mall in Washington, D.C., the United States, July 11, 2020. The number of COVID-19 cases in the United States reached 3,225,721 as of 3:34 p.m. local time on Saturday, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)

A social distancing sign is seen in the National Gallery of Art Sculpture Garden in Washington, D.C., the United States, July 11, 2020. The number of COVID-19 cases in the United States reached 3,225,721 as of 3:34 p.m. local time on Saturday, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)

People visit the National Gallery of Art Sculpture Garden in Washington, D.C., the United States, July 11, 2020. The number of COVID-19 cases in the United States reached 3,225,721 as of 3:34 p.m. local time on Saturday, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)

People visit the National Mall in Washington, D.C., the United States, July 11, 2020. The number of COVID-19 cases in the United States reached 3,225,721 as of 3:34 p.m. local time on Saturday, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)