efficient campaign machines (Score 1)

There's another possibility. The campaigns are smarter and better informed. Marketing, 'consumer' research, targeting are all advancing by leaps and bounds.

If you need 50.1% of the vote in order to win a particular state and you can show through your science of marketing that you probably have 51% why continue to spend money in that state???? Why throw away your money? Save it for an emergency. Need more money? fund raise some more. Have enough money? Sleep in and cuddle up with the soooooo sexy Laura Bush (mmmm mmm mmm) or go clear some brush.

An efficient machine doesnt waste resources (money, sleep, opportunities for sex and clearing brush) if it has already produced its output (an election win).

I'm not saying they have a perfectly tuned machine (clearly no one knows the outcome for certain). But I do think it's tending in that direction and we may rarely ever see 55%+ again.

Just a little theory.