Parsing Pennsylvania's Primary (or Nate Silver N'at)
One topic I've seen alluded to is straight up party switching among people already registered. This matters for Pennsylvania's closed primary. This is a map I concocted of the ratio of voters switching into the Republican and Democratic parties cumulatively since the beginning of 2016 (through April 3, and note the deadline to register for the primary election was March 28).
That may be a bit misleading if inferred to be a new phenomenon. Among already registered voters, party switching typical has this pattern or more switching to R than to D. Yet how is it Pennsylvania has roughly million more registered Democrats than Republicans, a gap that is expanding over the years, not contracting? The map above is only reflecting data of party switching among ready-registered voters who changed their party from something else to Democratic or from something else to Republican. A similar map showing the ratio of new registrations is below. This depicts the ratio of new registrations as Democrats as percentage of total (note the total is among those registering as D or R, so not reflecting registrations other parties, or to no party.)
Make of it what you want. Talk of Reagan Democrats and silent majorities I leave to the purely political pundits. The total number of party switching into a major party (D or R, the first map) added up to under 75 thousand voters this year. For a state with with over 8 million registered voters, you are really talking ~1%, much of which you would have expected no matter who was running this year. Maybe this does not capture trends late in 2015, but I doubt it would make much of a difference.