TREVOR HUNNICUTT, PATRICIA ZENGERLE and JARRETT RENSHAW DEMOCRAT Joe Biden was sworn in as president of the United States tonight, assuming the helm of a country reeling from deep political divides, a battered economy and a raging coronavirus pandemic that has killed more than 400,000 Americans. With his hand on an heirloom Bible that has been in his family for more than a century, Biden took the presidential oath of office administered by U.S. Chief Justice John Roberts just after noon (1700 GMT), vowing to "preserve, protect and defend the Constitution of the United States." Biden, 78, became the oldest U.S.…