President Trump at a meeting with Colorado Gov. Jared Polis and others in the Cabinet Room of the White House on May 13, 2020. | Doug Mills/Getty Images

“This isn’t even a debate in other places,” one expert says.

More than five months into the Covid-19 pandemic, the evidence for masks keeps getting stronger.

One study in Germany found that mask mandates reduced the growth of infections by about 40 percent. Another estimated that mask rules in 15 US states and Washington, DC, may have prevented as many as 230,000 to 450,000 cases. Meanwhile, evidence suggests protests against police brutality and racism in many cities this summer did not lead to big spikes in case counts, which some attribute to the fact that the demonstrations were outdoors and many participants were masked.

For all these reasons and more, many public health experts have