So, none of this is cannon, it comes from the novelization.
The President's name is John Harker, former Senator from Upstate New York.
Nicknamed "Mousey" or "Straddler" by both his colleagues and opponents.
He helped create the United States Police Force, made up of ex-soldiers returning from the war overseas.
They replaced local and state police forces and act as judge, jury and executioner out in the field.
He has a convenient way of making his opponents "dissappear" if they oppose any of his legislation; the most recent being a Senator from Alabama, whereupon the state found all of its government funding cut off and water rights restricted, leaving the people to starve/die of thirst.
He was on his way to the Hartford Summit with a tape describing a new type of "clean" nuclear fusion bomb that will kill all the people and animals but leave the infrastructure intact and ready to be inhabited again within a matter of months, if not weeks.
He was going to deliver an ultimatum to the Soviet Union and China, surrender and end the war, or watch your capitols be destroyed and your countries become part of the United States.