WASHINGTON - Election Day is three weeks from now, and unless something happens fast, this will be one of those once- or twice-in-a-generation elections when a party enjoys unbelievable gains or endures horrendous losses that prove to be the exceptions to Tip O'Neill's adage that "all politics is local." In midterm elections, Democrats last suffered such a defeat in 1994; for Republicans, it was 20 years before that in the Watergate election of 1974.