Williams did NOT compare Obama to Hitler. He used an analogy of Hitler and Netanyaho to illustrate how politically polarized he thinks Boehner and Obama are.
Let the boy sing his song
He most certainly did, albeit indirectly. Invoking "Hitler" to make a moral statement is so passe as to be meaningless were it not for the fact it can get one fired in a heartbeat. The mere fact the two names appeared in the same context is enough to drive PC wussies into cognitive contusions. Perhaps that was Williams' aim.