At Christ Hospital in Jersey City, patients hospitalized with coronavirus receive a battery of treatments that doctors hope will ease their suffering and save their lives. They are given oxygen. Steroid inhalers. High doses of vitamin C, thiamine and zinc. Even plain old aspirin, to name a few. Also provided to patients is hydroxychloroquine, a decades-old malaria drug thrust into the spotlight of the coronavirus pandemic by President Donald Trump. It unexpectedly joined the culture wars last month after Trump touted it as a potential “game changer,” though medicine has yet to determine whether it is effective in combating the...