The U.S. economy is slowing down after a burst of activity in May, said Dallas Fed President Robert Kaplan on Monday. "The economy did bottom in April, we started to grow again toward the end of April and certainly into May," Kaplan said, in a talk at the National Press Club. There was even a brief spell of "double-digit" growth that lasted until the second week of June, he said, but now growth is slowing down. Part of this is due to the resurgence of COVID-19, which is "muting growth," Kaplan said. He stressed that the public should wear masks, saying it "is the most important thing that can be done to make sure the rebound is faster, not slower." Kaplan is a voting member of the Fed's interest-rate committee this year.