Former Republican presidential contender Newt Gingrich, looking rested and at ease before TV cameras, had some succinct advice Sunday morning for Maryland Gov. Martin O'Malley, the head of the Democratic Governors Association, who often is mentioned as a possible 2016 candidate for the White House. “Raise a lot of money,” a smiling Mr. Gingrich told the governor on NBC’s “Meet the Press.” Mr. Gingrich, who dropped his own presidential bid earlier this month, showed flashes of why he briefly rose to the top of the Republican field, answering questions deftly and decisively, often squeezing in zingers while Mr. O'Malley stuck...