During a news conference Wednesday evening, President Trump said: "We don't have to test the entire state in the Middle West or wherever they may be. We don't have to test the entire state. I think it's ridiculous. A lot of those states could go back [to work] right now, and they probably will."
He's correct that the entire population of a state does not need to be tested right now. However, all 50 states do have cases, and those small- and medium-sized outbreaks may be growing exponentially.
So there is a vital need to test aggressively wherever the disease is spreading. That includes testing close contacts of those known to be ill, as well as broad testing in areas where the disease is spreading through the community and health officials are not sure of the source.
The president talks frequently about letting certain parts of the country get back to work. But if that is allowed to happen when the number of cases is still growing, those communities could well find themselves in the same situation as New York, Washington and parts of the San Francisco Bay Area, where the disease continues to spread.
As has already happened, a handful of cases can seem manageable at first, but if the disease spreads unconstrained, the disease will grow exponentially. If each sick person gives it to an average of 2.5 others, after 10 cycles of spread, a single case can lead to 9,500 cases.
Social distancing can reduce that 2.5 figure to slow the spread. But testing is an essential and powerful tool, as well.