The source of the hopes for a coronavirus cure should raise a lot of red flags. President Donald Trump’s daily press briefing on the coronavirus pandemic has been compared to many things: state propaganda, daily talk show, three-ring circus. It is somehow all of these things, but it is also something else: an infomercial. For the past two weeks, the president has been hawking a miracle cure: the antimalarial drug hydroxychloroquine. He has hailed it as “very encouraging,” a “phenomenal drug,” and “the biggest game changer in the history of medicine.” Trump has also portrayed it as a Hail Mary:...