From Holden:

Democratic party affiliation is rising.

During the month of June, 37.0% of Americans identified themselves as Democrats, up from 36.4% in May. Only once in the past year have a larger share of American adults identified themselves as Democrats.

The number of Republicans remained essentially unchanged—33.5% in June and 33.6% in May.

However, the number of Americans unaffiliated with either major party dipped to 29.5% in June. That’s down half a point from 29.5% in May.