4) Democratic territory has been reduced to the bastions of two core groups — black voters and gentry liberals. Democrats win New York City and the San Francisco Bay area by overwhelming margins but are outvoted in almost all the territory in between — including, this year, Obama’s Illinois. Governor Jerry Brown ran well behind in California’s Central Valley, and Governor Andrew Cuomo lost most of upstate New York.

Democratic margins have shrunk among Hispanics and, almost to the vanishing point, among young voters. Liberal Democrats raised money to “turn Texas blue.” But it voted Republican by wider-than-usual margins this year.

Under Obama, the Democratic base has shrunk numerically and demographically. With superior organization, he was able to stitch together a 51 percent majority in 2012. But like other Democratic majority coalitions — Woodrow Wilson’s, Lyndon Johnson’s, even Franklin Roosevelt’s — it has proved to be fragile and subject to fragmentation.