Back in April, President Trump picked out a single computer model of coronavirus spread as his oracle of choice. Unsurprisingly, that simulation initially had rosier estimates than other algorithms, projecting many fewer Covid-19 deaths — and its unconventional calculations and fluctuating estimates drew sharp criticism from epidemiologists. But the statisticians behind it have since changed their methods, and their new numbers, published Friday, bolster what scientists have long been saying: That doing away with social distancing measures could entail vast numbers of deaths, and that widespread mask-wearing in public could save tens of thousands of lives.