Who's in the most trouble in this fall's elections: a) liberals; b) Democrats; or c) incumbents? The answer: any combination of the three, according to pundits and poll watchers trying to explain today's primary upset of 16-year Oklahoma Congressman Mike Synar. In one of the biggest electoral turnabouts in the state's history, the 43-year-old Okie from Muskogee became the third House member to lose a primary this year. Voters fed up with the Clinton-like liberal handed 51 percent of the ballot to a 71-year-old retired school principal instead. BTW: How bad is it? Senate bigwig Tom Foley (Democrat, Washington) didn't even have an opponent, yet he pulled only 35 percent of the vote in his primary yesterday.