U.S. national flags fly at half-staff in Houston, Texas, the United States, on Aug. 5, 2019. Two mass shootings over the weekend in the United States left 31 people dead and dozens injured. On Sunday, U.S. President Donald Trump issued a proclamation, ordering that all American flags at military installations, federal facilities, and the White House be flown at half-staff until sunset on Aug. 8. (Photo by Lao Chengyue/Xinhua)