IF LATIN America is hard hit by the coronavirus epidemic, as it now appears it will be, two of its political leaders will bear outsize responsibility. Presidents Jair Bolsonaro of Brazil and Andrés Manuel López Obrador of Mexico govern the region’s two most populous countries by far, with more than 325 million people between them. Yet both have minimized the risk of the novel coronavirus and resisted — or even flouted — measures to prevent its spread.

Mr. Bolsonaro mingled with supporters at a rally as recently as Sunday, even though his own health ministry recommended that he isolate himself because he has had close contact with infected officials. At a news conference Wednesday, he warned against “hysteria” and said no one should be surprised to see him ride a crowded subway in Sao Paulo or a ferry in Rio de Janeiro. This weekend he is planning a two-day celebration of his 65th birthday.

Never mind that Brazil’s covid-19 case count had risen to 621 confirmed cases on Thursday, including the president of the Senate, national security adviser and other senior officials. Thanks to Mr. Bolsonaro, the federal government has taken few preventive measures, leaving borders, schools and businesses open. Though some state governors have stepped up and imposed closures, Brazil remains wide-open to the pandemic. No wonder hundreds of thousands of people in Rio de Janeiro and Sao Paulo banged pots and pans from their homes on Tuesday and Wednesday in protest.

Mr. López Obrador, a populist like his Brazilian counterpart, has been almost as heedless of the mounting threat. Mexico, as of Thursday, had 118 reported covid-19 cases, but the president was still resisting restrictions on travel and commercial activity. There are “pressures of all types,” he said Wednesday. “Close the airport, shut down everything, paralyze the economy. No.” He said his priority was to protect “all the people who work, who live by economic activity, by what they can get day to day.”

The concern for ordinary workers is understandable, especially in a country with a large informal economy. But Mr. López Obrador, like Mr. Bolsonaro, has been cavalier in his personal response to the virus, rejecting his health minister’s recommendation that he abstain from hugs and kisses. “You have to hug,” he said at a news conference this month. “Nothing is going to happen.” Last weekend, he acted on his words, plunging into a crowd and repeatedly kissing a baby. His government is following his lead, last weekend limiting some sports events and public gatherings but still allowing a large music festival to go forward in Mexico City.

These lax policies provided President Trump with some justification for his decision this week to curtail movement across the U.S.-Mexican border, including by asylum seekers. But Mr. Trump missed an opportunity to exert influence on Mr. Bolsonaro when he was asked Thursday about the latter’s dismissive approach to the epidemic. “I have no message for him” other than “he’s doing a good job in Brazil,” Mr. Trump said. In fact, Mr. Bolsonaro’s performance has been grossly irresponsible — and it soon may cost Brazil many lives.

Read more: