Everywhere you look -- Sonoma County, the North Coast, California and nationwide -- independent voters are on the rise.

By some accounts, nonpartisan voters now comprise the nation's largest party, outnumbering Democrats and Republicans.

In the past 50 years, voters who reject a partisan label have swelled tenfold from a relatively insignificant 2 percent to more than 20 percent of registered voters in Sonoma County and in the North Coast congressional district.

Most of that gain appears to come at the expense of Republicans, whose share of the electorate has dwindled by half -- from about 44 percent to 22 percent -- between 1962 and 2012, while the Democratic share has dipped a mere 3.5 percent in the district and 1.8 percent in the county.

In the past half-century, Sonoma County has gained 93,399 Democratic voters, 51,048 independents and only 25,909 Republicans.

Disaffection with partisan sniping and political gridlock is often cited as the catalyst for the swing to an apparent ideological middle ground.

But the rising independent tide includes a lot of what political consultant Mark Mellman calls "closet partisans," voters who actually hew toward one party or the other.

Various studies put the number of independents at 34 percent to 40 percent of the nation's electorate, Mellman wrote in an article last year in the Hill, a publication devoted to congressional politics.

But when asked which party they lean toward, "lo and behold, a great many of those who call themselves independents at first blush feel closer to one party or the other (a group we affectionately call 'leaners,')" Mellman said.

Moreover, they vote "very much like partisans," he said.

With leaners factored out, the number of "real independents" is 10 to 11 percent, Mellman said.

In California, independents "are more likely to lean Democratic than Republican," according to a Public Policy Institute of California report last month.

That tendency makes the state darker blue than it seems, boosting the Democratic voter registration advantage over Republicans from 13 points (43 percent to 30 percent) to 17 points (53 percent to 36 percent), the report said.

The partisan divide is also more polarized, with more Democratic voters calling themselves liberals and more Republicans identifying as conservatives now compared with 2000, it said.

You can reach Staff Writer Guy Kovner at 521-5457 or guy.kovner@pressdemocrat.com.