Democrats, for decades a heterogeneous and often fractious amalgam of voters, have become overwhelmingly liberal on cultural issues like gay rights and abortion. Their belief reflects a party now dominated by a socially progressive coalition of millennials, minorities and wealthy, educated whites, many of them secular.

This is the party of Barack Obama.

“The voters that President Obama brought into the process as activists have moved these issues forward in the Democratic Party,” said Anita Dunn, a former top aide to Mr. Obama. “He brought a great number of people into our coalition as participants, not just voters, which has really helped bring a degree of cohesion around these issues.”…

“After a generation of Republicans using social issues as a club over the head of Democrats, they now work in Democrats’ favor,” said Doug Sosnik, a longtime Democratic strategist.