McCain, a conservative and ranking Republican on the Senate Armed Services Committee, said a plan to ensure fair elections in the fall needed to be laid out promptly and stuck to in order to ensure the Egyptian people their grievances were being addressed.
"There is also a good chance for a real functioning democracy and arguably the most important nation in the middle East," McCain said on CNN's "State of the Union."
McCain said the United States had been prodding Mubarak for years to loosen his grip on power and warned that the longer an authoritarian regime hangs on, the more dramatic their fall can be.
Longtime U.S. diplomat John Negroponte told CNN Sunday that Mubarak's run had already effectively come to an end.
"I think it's now about how that era comes to a close," said Negroponte, the U.S. ambassador to the United Nations under President George W. Bush. "I think it's all about the nature of the transition of power and how that's arranged."