Among Democrats, support for same-sex marriage rose from 59% in April to 65% in the latest poll, conducted from June 28 to July 9. Among liberal Democrats, the increase was a notable 10 percentage points, from 73% to 83%.

Otherwise, opinions have scarcely budged. Neither Republicans nor political independents have significantly changed their views.

"Pretty much however we split it ... the change is really focused among Democrats, and especially liberal Democrats," said Besheer Mohamed, a research associate at Pew.