By Charles Lam

While Asian Americans make up 4.1 percent of of voting-age citizens in the U.S., they are the fastest growing racial group in the country, according to the Pew Research Center.

Researchers expect the voting bloc to double by 2040, and Asian-American voters could end up swinging 27 congressional races this year, according to AAPI Data, a research program at the University of California, Riverside.

Here are 10 congressional races where Asian-American candidates or voters could have a particular impact.

Arizona’s 8th Congressional District

While Asian-Americans represent only 4.2 percent of residents in Arizona’s 8th Congressional District, the race just northwest of Phoenix pits incumbent Republican Rep. Debbie Lesko against Democrat Hiral Tipirneni, a medical doctor.

Image: Dr. Hiral Tipirneni speaks with supporters
Democratic candidate for the Arizona 8th Congressional District Dr. Hiral Tipirneni, center, talks with supporters at a local restaurant in Sun City, Arizona, on April 10, 2018.Ross D. Franklin / AP

The two last faced off in an April special election, with Lesko beating out Tipirneni 52 to 48 percent in a bid to finish the term of former Republican Rep. Trent Franks, who resigned after revelations that he had asked a staffer to be a birth surrogate.

The Cook Political Report currently rates the race "likely Republican." Tipirneni has outraised Lesko $4.1 million to $1.9 million, according to October Federal Election Commission filings (FEC). The district went for President Donald Trump over Hillary Clinton in the 2016 general election, 46 percent to 43 percent.

California’s 39th Congressional District

One of the most competitive district in California, this race pits Republican Young Kim against Democrat Gil Cisneros in an open district that is more than 31.4 percent Asian American.

Kim has solid experience in the district, formerly representing a portion of it in the state legislature and previously working for its current representative, Republican Ed Royce, who decided not to run for re-election.

The Cook Political Report rates the race a toss-up, one of three in the former GOP stronghold of Orange County, which went for Clinton over Trump, 51 percent to 42 percent. Cisneros has raised $11 million, $8.8 million of which were loans by the candidate, according to FEC filings. Kim has raised $2.5 million.

“I have been out there, I know the district, and my personal story and experience as an immigrant, as well as work ethic, sets me apart from the rest of the field,” Kim told NBC News in May.

“We had a tremendous amount of luck and good fortune," Cisneros told NBC News in September. "And we used that in a way that we could give back and create opportunity for others through education, the same way I received that opportunity."

California’s 45th Congressional District

Asian Americans make up 25.7 percent of the population in this Southern Orange County Congressional District, where incumbent Republican Rep. Mimi Walters faces Democrat Katie Porter, a law professor at the University of California, Irvine.

The Cook Political Report rates the race a toss-up. The county went for Clinton over Trump, 51 percent to 42 percent. Porter has raised $5.8 million compared to Walter’s $4.4 million.

California’s 48th Congressional District

In California’s 48th Congressional district, which includes portions of Little Saigon and where about 18 percent of the population is Asian American and about 10 percent Vietnamese American, 30-year incumbent Republican Rep. Dana Rohrabacher faces off against Democrat businessman Harley Rouda.

Vietnamese Americans skew more conservative than other Asian-American groups — in a 2018 survey, 42 percent identified as Republicans, 28 percent as Democrats and 28 percent as independent — and some experts say the community is growing increasingly more politically savvy.

“There’s potential for swing voters,” Linda Trinh Vo, a professor of Asian-American studies at the University of California, Irvine, said in October. “Vietnamese Americans can make an incredible difference in close elections, and we’re seeing that in Orange County.”

The Cook Political Report rates the district a toss-up.

Rouda has made Vietnamese-language canvassing a part of his electoral strategy. Rouda has raised $7.3 million, $1.6 million of which were loans. Rohrabacher has raised $2.4 million.

“Every vote matters in the district, and for a guy who won the second seat in the primary by 125 votes out of 175,000, I’m not taking anything for granted,” Rouda said in October. Rohrabacher did not respond to a request for comment at that time.

Georgia’s 7th Congressional District

Georgia’s 7th Congressional District, where seven-year Republican incumbent Rep. Rob Woodall faces Democrat Carolyn Bourdeaux, an associate professor of at the Georgia State University’s Andrew Young School of Policy Studies, features a population that is 14.1 percent Asian American. The Northeast Atlanta-area district is also majority-minority, with non-Hispanic whites making up 45 percent of the population.

Bourdeaux has raised $2.4 million compared to Woodall’s $1 million. Gwinnett County, one of two in the 7th District, went for Clinton over Trump in 2016, 50 percent to 44 percent. Forsyth County, the district’s other county, went for Trump over Clinton 70 percent to 23 percent.

The Cook Political Report rates the race "lean Republican."

Nevada’s 3rd Congressional District

Democrat Susie Lee and Republican Danny Tarkanian face off for an open seat in this district south of Las Vegas as incumbent Democrat Rep. Jacky Rosen is running for the Senate. Asian Americans and Pacific Islanders make up about 15.5 percent of the population in the district; Lee has said she has hosted events and roundtables in the community.

“The biggest thing is them seeing that you’re there, and that you’re listening and that you’re involved,” she said in October. Tarkanian did not respond to requests for comment at the time.

Lee has raised $4.6 million compared to Tarkanian’s $2.2 million, $215,000 of which were loans by the candidate. Clark County, where the district is located, went for Clinton over Trump in 2016, 52 to 41 percent. The Cook Political Report rates the race "lean Democratic."

New Jersey’s 3rd Congressional District

Democrat Andy Kim — a former member of the Obama White House — and three-year incumbent Republican Tom MacArthur face off in this South New Jersey district, where Asian Americans make up 3.5 percent of the population.

If Kim were to win, he could be the first Korean American in Congress since 1999.

“September 11th happened during my time in college,” he told NBC News in August. “And that was really something that had motivated and pushed me and many in my generation to think about ways in which we can be of service.”

Kim has raised $5.2 million compared to MacArthur’s $4.4 million, $1.4 million of which were loans by MacArthur. Burlington County, one of two in the district, went for Clinton over Trump, 55 percent to 40 percent. Ocean County, the other county in the district, went for Trump over Clinton, 65 percent to 31 percent. The Cook Political Report rates the race a toss-up.

Ohio’s 1st Congressional District

Democrat Aftab Pureval faces incumbent Republican Rep. Steve Chabot in this district, which includes much of Cincinnati and where Asian Americans make up 3.7 percent of the population. Chabot represented the district from 1995 to 2009, losing an election in 2008. He regained the seat in 2010 and has represented the district since.

Pureval has raised $3.5 million compared to Chabot’s $1.5 million. The district voted for Trump over Clinton, about 51 percent to 44 percent.

The Cook Political Report rates the race "lean Republican," but Pureval’s campaign has seen staff turnover in recent days. Pureval has fired two staff members and accepted the resignation of his campaign manager, NBC affiliate WLWT reported Wednesday.

Pureval’s campaign has faced accusations of unlawfully spending money from a state campaign for Pureval's congressional race as well as accusations that a staff member infiltrated his opponent’s campaign, according to WLWT. Pureval has said he received legal advice regarding his campaign spending, WLWT reported, and would return that money if the spending was found to be wrong.

Texas’ 22nd Congressional District

Democrat Sri Preston Kulkarni, a former member of the U.S. diplomatic service, faces off against nine-year incumbent Republican Rep. Pete Olson in this district southwest of Houston, where Asian Americans make up 19.2 percent of the population.

Kulkarni has made reaching out to a diverse group of voters a core part of his campaign, which he said in October can reach out in more than a dozen languages.

“I said, maybe they don’t vote because we don’t bother,” Kulkarni recalled in September, referring to advice he received about Asian-American voter outreach. Olson did not respond to a request for comment at the time.

Olson has raised $1.4 million compared to Kulkarni’s $1.2 million. Fort Bend County, which makes up a majority of the district, went for Clinton over Trump 51 percent to 44 percent. The Cook Political Report rates the race "lean Republican."

Virginia’s 10th Congressional District

Democrat Jennifer Wexton, a state senator, faces off against three-year incumbent Republican Barbara Comstock in this district west of Washington, where Asian Americans make up 15.8 percent of the population.

Wexton has raised about $5.4 million compared to Comstock’s $5.8 million. Clarke, Frederick and Loudoun counties, which the district contains, were split between Clinton and Trump. Clarke and Frederick voted Trump over Clinton, 65 percent to 30 percent and 57 percent to 38 percent respectively. Loudon County went for Clinton over Trump 55 percent to 39 percent. The Cook Political Report rates the race "lean Democratic."

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Allyson Escobar contributed.