I always wonder how far in advance show runners and writers know they are going break these events in a "President" series.
  1. The Assassination Attempt
    Starting with the most obvious. This is going to happen at some point. This could actually snowball in to the next one...
  2. Invoking the 25th Ammendment
    When the president is unable to perform his duties so the VP takes over. The VP will probably be in over his/her head.
  3. The Leak
    Someone on the President's senior staff will leak classified information.
  4. The Election
    Another obvious one but if the show goes on at least 4 years then your hand is forced.
  5. A Security Threat in the West Wing
    It'll probably end up being nothing but it's a solid plot device for getting groups of people who don't interact much or who are having a conflict to be stuck in "lock down" together.