 Complete the following phrase:  A pair of conflicts ensued over Lenos 22-year tenure, both revolving around the then-current hosts of Late Night, the program directly following Tonight since its premiere in 1982. Original Late Night host David Letterman was considered Carsons top choice as successor and left the network acrimoniously in 1993 after Leno was given the job. Years later, NBC attempted to transit Lettermans Late Night successor, Co OBrien to in turn succeed Leno as host of Tonight in 2009. However, as a result of various contractual obligations and fears of losing performers to other networks, Leno was given a nightly prime-time show shortly after Cos run began. Leno posted less than stellar ratings, leading to a domino effect on the late local news. OBriens Tonight also suffered falling ratings leading to a 