(Bloomberg Opinion) — This is a market for Warren Buffett, and U.S. investors sure could use some of his positive vibes right now. So where is America’s biggest booster and hungriest dealmaker?Buffett, the chairman and CEO of Berkshire Hathaway Inc., has been noticeably quiet since an explosion in coronavirus cases sent much of the populace into self-isolation and the country hurtling toward a recession. New York City, the capital of finance, is the new epicenter of the outbreak. But even 1,200 miles west in Buffett’s more airy state of Nebraska, the number of known infected residents is approaching 200, showing just how widespread it’s become.Buffett’s age — he’ll turn 90 in August — puts him among those most at risk of severe complications from the virus. (He was also treated for early-stage prostate cancer in 2012.) It