The California Democratic Party added about 700,000 voters between January and July of this year, a 10 percent increase that is significantly higher than the rise in registered Democrats during previous presidential elections, according to new data from the California Secretary of State.
The Republican Party in California added about 130,000 voters, a 3 percent increase, between January and July. The number of voters not stating a party preference rose by about 70,000, or 2 percent. The number of third-party voters fell by about 90,000, or 10 percent.
Much of the increase in party registration seems to have come from the ranks of those not already registered to vote. Overall, the number of Californians registered to vote increased by about 825,000 between January and July to 18.1 million. That equates to 73 percent of California adults eligible to vote.
About 45 percent of registered voters in California are now Democrats, the highest proportion in more than a decade.
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Because the Republican Party expanded at a rate slower than the statewide average, the percentage of California voters registered as Republican fell to 27 percent, the lowest proportion in more than a decade.
In 2008, when Barack Obama created excitement among California Democrats, party registration increased by about 465,000, or 7 percent, between January and September. Democratic Party registration increased by less than 1 percent between January and September of 2012.
A couple of factors are likely behind this year's increase.
Hundreds of thousands of Californians took a keen interest in the primary race between Hillary Clinton and Bernie Sanders. Sanders' campaign portrayed the California primary as vital - a last chance for a comeback.
Some of the counties with large increases in registered Democratic voters also have a large Latino population. Republican nominee Donald Trump has made immigration a key part of his platform, vowing to build a wall to keep out undocumented immigrants.
Merced County, where six out of 10 residents are Latino, saw a 20 percent increase in registered Democratic voters, more than any other county in the state. San Bernardino County, where half of voters are Latino, saw a 16 percent increase. Even so, some places with relatively small Latino populations like Nevada and Trinity counties also saw big increases in Democratic registration.
This chart shows registration by party in January and July of this year. The map shows where Democratic Party registration has increased the most during that period.