Is This Year 2004 — or 1980?

All presidential campaigns are unique. Candidates’ characters, economic and political circumstances and “October surprises” combine to make these races the most unpredictable U.S. elections.

Certain constants, however, remain — common threads in political tactics, momentum, economic yardsticks and public attitudes. This is especially true in reelections. Not surprisingly, voters cast their ballots based largely on their view of a president’s performance. High approval ratings can almost guarantee reelection. Incumbents who don’t poll at least 50 percent face serious risk.

This year’s campaign offers striking similarities to two recent campaigns involving incumbents — with very different results. One brought President George W. Bush another four years in the White House, one sent President Jimmy Carter back to Georgia.