The latest Gallup Poll finds that loyalty to the Democrats and Republicans is at or near historic lows. In 2015, for the fifth straight year, "at least four in 10 U.S. adults identified as political independents," a Gallup spokesman said. Forty-two percent said they were independent last year; 43 percent listed themselves that way in 2014, reflecting little change.

Twenty-nine percent said they were Democrats and 26 percent said they were Republicans.

The Democrats' share was the lowest for that party in Gallup's 65 years of asking about party identification. The previous Democratic low was 30 percent in 2014.

The Republicans also have cause for concern. The 26 percent who identified with the GOP was just 1 percentage point higher than the historical Gallup low of 25 percent self-identified Republicans in 2013.

