Millions of Americans holed up at home against the coronavirus Monday, with many of them thrown out of work until further notice, as authorities tightened the epic clampdown and the list of businesses forced to close across the U.S. extended to restaurants, bars, gyms and casinos.With the U.S. economy shuddering to a near-halt, the Dow Jones Industrial Average plummeted nearly 3,000 points, or 13%, its biggest one-day percentage loss since the Black Monday crash of 1987.The rapid work stoppage had Americans fretting about their jobs and their savings, threatened to overwhelm unemployment benefit programs, and heightened fears the country could plunge into a recession.President Donald Trump acknowledged that possibility for the first time and suggested the nation may be dealing with the virus until July or August.The number of infections in the U.S. climbed to nearly 4,500, with at least 80 deaths, two-thirds of them in hard-hit Washington state, where