EVEN WITH the daily tally of new covid-19 cases flat or rising in nearly 40 states, Republican and Democratic governors, under pressure to restart their economies, are relaxing lockdown orders. Often they are doing so in the absence of basic data that would shed light on the pandemic’s dimensions; many of the states that are reopening most aggressively have also done the least testing on a per capita basis, meaning none has a good fix on the pandemic’s spread. That amounts to an epic gamble with the lives of residents.

Examples include Texas, where tanning salons and other businesses are now open, even though the spread of covid-19 has plateaued at more than 1,000 new cases daily after a stay-at-home order that lasted barely a month; Missouri, where most businesses and large public venues were allowed to reopen last week, despite a rising seven-day average of new cases; and South Carolina, where retail stores and other establishments began reopening last week, even though the covid-19 caseload has barely declined in more than a month.

Complacency may be driving decisions in those states, where the disease’s death rates per 100,000 people — 4 in Texas, 6 in South Carolina and 8 in Missouri — are among the nation’s lowest. As in the investment world, however, past results with the pandemic are no guarantee of future performance.

The trouble with restarting the economy in states where testing is scant — and contact tracing inadequate, as it is nationwide — is that the risk of a spike in infections and deaths is incalculable. And while the daily death count from the disease has dipped in recent days, no governor has offered a prospective accounting of how much new sickness and death would trigger a rollback of the reopening, or what level of gross domestic product and employment growth would justify a new surge of infections.

Ohio Gov. Mike DeWine wrestled with that calculus before he announced that some personal service businesses in the state can reopen this Friday, and restaurants for dine-in service, with restrictions, the week after that. Ohio, it is worth noting, is among the nation’s least-tested states on a per capita basis. “The more contacts we have, the more we do, there is more risk,” said Mr. DeWine, a Republican who was the first governor to order schools closed. “This is a new gamble. . . . We don’t want to see a spike.”

The governor’s anxiety about reopening, and possibly his misgivings, were apparent from his remarks. No doubt he knows the peril posed by the hodgepodge of state decisions to reopen quickly, gradually or not at all yet — the product of an absence of leadership from President Trump, who has ignored the White House’s own guidance to states on reopening. By moving too fast, any one of those states, or several, may represent a hole in the fence that may have begun, barely, to contain an outbreak that has already killed roughly 80,000 Americans. The result is a potentially deadly game of trial and error.

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