IF THE US had a parliamentary system, the Clinton presidency would already have been consigned, in Augustine Birrell's felicitous phrase, to the great ash heap called history. In parliamentary systems, the head of government and head of state are different offices. In parliamentary systems, heads of government must maintain the confidence of their legislature, and of their party. Usually they're elected for fixed terms or, in constitutional monarchies, until they die or abdicate. And when they do go, the impact on policymaking is usually minimal.
Heads of government are a different story.
They must maintain the confidence of their legislature, and of their own party. If they don't, they're out. New Zealand Prime Minister Jim Bolger was recently deposed in a Cabinet coup for the horrific sin of being unpopular with the electorate. Others, like Canada's Brian Mulroney and Britain's Margaret Thatcher, met the same fate, although sometimes with the face-saving facade of voluntary resignation. Think of poor Willy Brandt, who had the misfortune of having an East German spy as a top adviser.