A ballot is placed into a locked ballot box in San Diego. (Mike Blake/Reuters)

Can Democrats flip congressional seats in some of California’s traditional Republican strongholds, to help them retake the U.S. House? They’re pouring resources into seven congressional races in California, hoping to ride the potential “blue wave.” These swing districts include a growing base of Asian American voters, nearly a third of whom identify as independents. These votes will be important to candidates in California’s June primary since the top two vote-getters — regardless of party — will advance to the general election.

In several of these targeted districts, Asian Americans accounted for nearly 15 percent of the 2016 electorate. So how do Asian Americans lean?

For three of these districts, I examined their registration and voting patterns, finding that although many Asian Americans in the districts lean Republican, an unusually large percentage voted for Hillary Clinton. What might that mean for California’s primary next month?

How I did my research

I used the statistical method of ecological inference, which is a method required by the courts in Voting Rights Act cases, to estimate how support for a candidate varied by race and ethnicity. I turned to district demographic information and vote totals, and used surname-matched voter data available from California’s Statewide Database at the University of California at Berkeley’s School of Law, which identifies Asian American voters from six national origin groups — Chinese, Indian, Filipino, Korean, Japanese and Vietnamese.

Southern California Asian Americans have generally voted Republican — but in 2016 they went for Clinton

In several of the Southern California districts that Democrats are trying to flip, Asian Americans have traditionally leaned Republican. Nationally, Asian Americans have been found to lean Democratic, as they do in northern California, but it’s the opposite in Southern California. In Orange County, registration patterns show Asian Republican registrants outnumber Democratic registrants. In California’s 39th Congressional District, longtime Republican lawmaker Edward R. Royce recently announced his retirement; 17 candidates are running for his seat. In this district in 2016, 15.2 percent of voters were Asian Americans, including 16,373 Chinese Americans, 6,607 Korean Americans, 5,244 Filipino Americans and 4,048 Indian Americans. More than a third of Asian Americans were registered as independent.

Similarly, the 48th Congressional District has been held by Republican Rep. Dana Rohrabacher since 1988. In 2016, Asian Americans accounted for 12.3 percent of the electorate. Of these, 57 percent are Vietnamese Americans, long considered the most conservative of Asian Americans: In 2016, twice as many registered Republican Vietnamese voters (8,351) cast ballots in the district than did Vietnamese Democrats (4,956). A majority of the Asian American voters in these two districts supported Republicans Royce or Rohrabacher for the past several election cycles.

And yet in 2016, Asian Americans in these districts supported Clinton over Trump. That’s consistent with national surveys, which show a majority of Asian Americans supported Clinton. At the same time in these districts, they still voted for their Republican incumbents. In the 39th, 61 percent supported Royce, while 68 percent supported Clinton. In the 48th, 58 percent supported Clinton, while 66 percent supported Rohrabacher.

Vietnamese American voters in the 48th were less conservative in 2016 than their party registrations might suggest: 75 percent voted for Clinton, and they were evenly split between supporting or rejecting Rohrabacher.

Asian Americans tend to vote for other Asian Americans, regardless of party

June’s primary races might turn on whether Asian candidates are on the ballot. In the 39th Congressional District, Asian Americans consistently supported Royce — except in 2012, when the Chinese American Democrat Jay Chen was running. Chen got 62 percent of the Asian American votes generally and an impressive 95 percent of Chinese American votes. Democratic candidate Andy Thorburn leads the district’s candidates in campaign contributions, according to Ballotpedia. But if the 2012 race is a clue, Asian Americans may well vote for either Korean American Young Kim, a former Republican state legislator, or Vietnamese American Democrat Mai Khanh Tran.

In 2012, in California’s 45th District, 98 percent of Asian American voters supported Democrat and Korean American Sukhee Kang, mayor of Irvine — although Republican incumbent John Campbell still won the district overall. In the upcoming primary, that Asian American preference may help Korean American Dave Min, who is endorsed by Democrats, advance to the general election.

Asian American voters are rapidly becoming a larger share of California’s voters

Asian Americans are the nation’s fastest-growing immigrant group. By 2040, according to the California Civic Engagement Project at the University of California at Davis, the number of California’s eligible Asian American voters is projected to increase 37 percent. In Orange County in 2008, Asian Americans made up just 2.1 percent of the electorate; by 2016 that had nearly tripled to 6 percent.

In a hotly contested election year, Asian American voters may make a significant difference.

Sara Sadhwani is a PhD candidate in political science at the University of Southern California.