When Lincoln Riley left Oklahoma for USC, the expectation was simple. He was supposed to restore one of college football’s most iconic programs and turn the Trojans back into a national championship contender. Four years later, that still has not happened. USC has shown flashes under Riley, particularly offensively, but the program continues to fall short of the standard that comes with coaching in Los Angeles. A 35-18 record is respectable at many places. At USC, it creates frustration, especially considering Riley’s reputation as one of the top offensive minds in the sport. The Trojans did improve last season, finishing 9-4 after going 7-6 the year before. The offense looked explosive once again, ranking No. 9 nationally in total offense and No. 13 in scoring offense. That side of the ball has rarely been the issue under Riley. Southern California Trojans head coach Lincoln Riley watches from the sidelines.…