Why? It’s impossible to know for certain with a virus as complex and unknown as this one. But there is an obvious potential cause: Many political leaders in the United States, including President Trump, are not following the advice of public health experts.

Those experts have urged a range of measures: continued social distancing until the number of cases falls further; a rapid expansion of virus testing; and planning an extensive program of “contact tracing” and quarantining, to allow for gradual reopening. The United States is taking some of these steps, but only some.

In the meantime, Trump is also encouraging protests that defy social distancing, which will only spread the virus. And he is calling for an across-the-board reduction in immigration, which will do little if anything to reduce the virus’s spread.

Some states are also taking counterproductive steps. Wisconsin’s insistence on holding an election in the midst of a pandemic has evidently led to some additional cases, as Alison Dirr of the Milwaukee Journal Sentinel reported.

So maybe we shouldn’t be surprised that the United States isn’t reducing the spread of the virus as well as many other countries. We don’t seem to be trying as hard.

If you are not a subscriber to this newsletter, you can subscribe here. You can also join me on Twitter (@DLeonhardt) and Facebook.

Follow The New York Times Opinion section on Facebook, Twitter (@NYTopinion) and Instagram.