The South Carolina primary is poised to dramatically alter the Republican nomination contest, winnowing and clarifying the largest and most rambunctious GOP field in decades. Many in the party's upper echelons have grown impatient with their splintered field of center-right, mainstream contenders and say they intend to put pressure on whichever candidate falls short of third place on Saturday night to quit. "South Carolina will reshape the race," said Scott Reed, the chief political strategist at the U.S. Chamber of Commerce. "Only the top three finishers will have a true narrative to continue down the road." South Carolina has a...