In an analysis by election expert, Rhodes Cook, for Virginia Professor Larry Sabato’s Crystal Ball report (July 12, 2018), Democrats now have a 12 million-vote advantage in the 31 states that register voters by party. Current vote percentages are 40 percent Democrat, 29 percent Republican and 28 percent independent.
The shift since 2000 in registration has been toward independents, with both Democrats and Republicans losing adherents.
Cook points out that in state-level analyses, about 70 percent of the time, the party dominant in registration wins the electoral vote. But, Donald Trump produced a number of anomalies where he won in spite of a Democratic registration advantage, including Florida, North Carolina and Pennsylvania.
He won the Pennsylvania of Colorado, Pueblo County, by 390 votes in spite of a 15,000-vote Democratic registration advantage.