In Gallup's most recent analysis, 42 percent of Americans identify as independent, compared with 29 percent who say they are Democrats and 26 percent who say they are Republicans.
(That shift has given Bernie Sanders the edge in our "Who is more popular, Trump or Sanders" tracker — at least for now.)
What's interesting is when you break out those independents. As we noted in August, most independents lean toward one party or the other — and in 2012, the majority of those leaning independents voted for their preferred party's presidential candidate. (According to the book "The Gamble," 90 percent of Democratic-leaning independents backed Obama in 2012, and 78 percent of Republican-leaning ones backed Romney.)
So an accurate picture of the electorate looks a bit more like the graph at right below than the one at left.
Since 2004, the number of what we'll call "pure" independents — which is to say, those who aren't leaning in one direction or the other — has increased slightly.
You can see the trend a bit more clearly looking only at the first Gallup surveys of each year. The lighter blue and red sections have gotten bigger, as have the yellow.
This is a long-term trend, but it clearly overlaps with what we're seeing in the presidential race. People may consistently vote for Republicans, but they would rather call themselves "independents." There's an appeal to being an outsider and to outsider politics that's reflected in how people see themselves.
But when the general election rolls around, those Republican-leaning independents will very likely vote for the Republican.