Hmmm...

Brad DeLong points to a pattern:

In 1972, we reelected an incumbent. In 1976, we elected an unknown southern governor who had not spent a day in Washington D.C. and had no national political record. In 1980, we elected an unknown governor--a southerner, if Orange County is "southern"--who had not spent a day in Washington D.C. and had no national political record. In 1984 we reelected an incumbent president. In 1988 we elected an incumbent vice president. In 1992 we elected an unknown southern governor who had not spent a day in Washington D.C. and had no national political record. In 1996 we reelected an incumbent. In 2000 we elected an unknown southern governor had not spent a day in Washington D.C. and had no national political record.

The pattern is clear: when there isn't an unknown southern governor running, an incumbent president can win reelection or an incumbent vice president can win election; but the unknown southern governor without a national political record wins the presidency--always.