Lately, no pollster has exactly covered themselves with glory in terms of predicting electoral politics, but one of the things pollsters can be useful for is measuring the attitudes of Americans over the long term. Gallup has been in business longer than any of the other players out there, so they are able to measure long-term trends more effectively than other companies. And what they are finding is that fewer people self-identify as Democrats than ever before - or at least since Gallup began asking the question in 1951.
At present, 29 per cent of Americans self-identify as Democrats, which is the lowest figure ever recorded. As Politico notes, prior to 1988, that figure had never fallen below 37 per cent. Truly, the presidency of Reagan ushered in a fundamental reorganization of American politics. Since the end of Reagan's term, Democrat self-identification has been on a steady downward slide.
Republican self-identification is also near historic lows at 26%; however, Republicans have not had as far to fall. Further, the fact that Independent self-identification has been on the steady rise masks the fact that those Independents have come to vote overwhelmingly Republican.
The facts on the ground are that beyond their self-identified voting base, the Democrats do a miserable job of attracting voters. They need committed Democrats to stand a chance to win. Believe it or not, but here in 2016, we are probably seeing the all-time post-Reconstruction high water mark for the GOP, with Republicans claiming over 60% of state legislatures, over 60% of state governorships, and both houses of Congress. The only office the Democrats have left is the Presidency and they look prepared to throw that away by nominating an unlikeable harpy who may well be under indictment for a portion of the electoral contest.
The end result of a world in which both Republican and Democrat self-ID continues to plummet is a world in which Republicans continue to win elections.