At this point, Obama's call for Mubarek not to run again -- which Mubarek has apparently agreed to -- is about the minimum reponse that he could have made under the circumstances. Obama might as well have asked Mubarek to resign now, since he had already committed the U.S. to oppose Mubarek as President. In fact, it probably would have been the correct move since the Egyptian oppositioin is demanding that Mubarek step down now, and, given the non-support of even the military, he will more than likely have to accede to this demand.
As I have suggested in a recent blog, the U.S. has managed to be on the wrong side of many popular movements to institute democracy. Even in Egypt, we probably could have had Nasser as a friend if we hadn't, as was usual for us, identified him as undependably nationalist, unaligned, and possibly leaning toward the U.S.S.R. This policy decision of J. F. Dulles turned out to be, at least partially, self-fulfilling, as Nasser turned around and accepted economic aid from the Soviets.
If Mubarek remains in office until September, it would give him time for all sorts of election-rigging, possibly in favor of his son. He should resign now, there should be a caretaker government, and internationally supervised elections in the Fall. The U.S. should take this position while there is still time -- before events overtake us.