A few factors have increased the chances of a multi-ballot convention.... 17 candidates entered the race and 15 remain. ...five contenders who today appear to have the message, money, organization and poll numbers to play the long game: neurosurgeon Ben Carson, real-estate magnate Donald Trump, Sens. Marco Rubio and Ted Cruz, and former Florida Gov. Jeb Bush. What complicates the picture is the GOP’s rule requiring the 28 (states+) that vote before March 15 to award their delegates proportionally. The exception is South Carolina, whose winner-take-all primary was grandfathered in. Add in the eight states voting on or after March...