What are the Differences between the British Prime Minister and the American President?

-The PM is the head of Government but not the Head of State. The President is both the Head of Government and State -The President has a Direct Mandate from the People, whereas the PM holds Power only by Leading the Main Party -The PM heads the Executive, but the Cabinet is Collective and can Force the PM out of his Job. The President is the Executive and the Cabinet is only the Advisory -The President is Bound by a Written Constitution limiting their Powers and their Impeachment. The Unwritten Constitution in Britain gives the PM Flexibility in Power -The UK is a Unitary State, giving the PM Power over the Entire Nation, where as the President shares Sovereignty with the Other Branches of Government and the States