The general election for president is predictable from the fundamentals (for individuals and at the aggregate level), primaries not so much.
Presidential general election campaigns have several distinct features that distinguish them from most other elections:
1. Two major candidates;
2. The candidates clearly differ in their political ideologies and in their positions on economic issues;
3. The two sides have roughly equal financial and organizational resources;
4. The current election is the latest in a long series of similar contests (every four years);
5. A long campaign, giving candidates a long time to present their case and giving voters a long time to make up their minds.
More details at my NYT column.