Lynn Vavreck at NYT’s The Upshot:

Donald Trump has confounded politicians, pundits and political scientists as he runs a most unconventional — and so far successful — campaign to win the Republican presidential nomination. Here’s the way we think these things are supposed to play out: Party leaders shape and guide the nomination process. We call it the invisible primary, and it was described in an influential 2008 book, “The Party Decides.” I asked David Karol, a University of Maryland associate professor of political science and one of the book’s four authors, whether Mr. Trump’s rise reveals a fundamental shift in party control. He thinks not. Here’s our conversation, slightly edited.