The GOP pack leader promises to stay in the 2016 race because he ‘NEVER gives up.’ But his business deals show a knack for spotting a coming decline. After sending mixed signals about what might drive him to withdraw from the presidential race, Donald Trump settled on a definitive answer last month: “I’m never dropping out.” The next day, he tweeted, “I’m leading big in every poll and we are going to WIN! Remember, Trump NEVER gives up!” But, like many successful businessmen, the real estate developer and GOP pack leader—who often espouses his disdain for “losers”—does not see every...