Because the undecided voter, or the one who switches party affiliations, is practically extinct. If in the past about 10 percent of voters were tossups, or even

Because the undecided voter, or the one who switches party affiliations, is practically extinct. If in the past about 10 percent of voters were tossups, or even just not 100 percent confident, today a much smaller portion are. So as party lines grow firmer, margins grow narrower.