Markets not merry as stock losses extend into eighth day

(Reuters) - A gauge of stocks worldwide posted an eighth straight decline on Monday as investors ignored Trump administration attempts to reinforce confidence and the U.S. president called the Federal Reserve the "only problem our economy has."Investors, also facing the likelihood of a prolonged U.S. government shutdown, fled to the relative safety of bonds and gold during the first day of a week of trading shortened by the Christmas holiday. Oil prices, meanwhile, tumbled more than 6 percent on..