But recent polls show Ms. Hirono pulling away with as much as a 22-percentage-point lead over Ms. Lingle, meaning Democrats can probably breathe easier that they won't lose a seat in a reliably blue state that also happens to be President Barack Obama's boyhood home.
That isn't the case in many other parts of the U.S. Seven Senate seats now held by Democrats—Connecticut, Missouri, Montana, North Dakota, Ohio, Virginia and Wisconsin—are rated as toss-ups by Real Clear Politics, a political website. With Democrats holding a slim 51-47 majority plus two independents who caucus with them, control of the Senate is at stake in the outcome of these races.
Although the Hawaii Senate race isn't as uncertain, Democrats here aren't taking anything for granted—a sign of how seriously the resurgence of the Republican Party is being taken even in blue strongholds.
The Democratic-backed Majority PAC just put more money for television advertising supporting Ms. Hirono, to counter a similar move by the Republican-backed Fund for Freedom Committee last week, said a Hirono aide. A spokesman for Majority PAC couldn't be immediately reached. Supporters of Ms. Hirono have spent the past several weeks working phone banks, waving signs on street corners and getting people to meet their candidate at campaign events.
"We are making sure the congresswoman gets out here as much as possible," said Betsy Lin, Ms. Hirono's campaign manager. "We are cautiously optimistic."
Another reason this race is being watched closely is that this is the first time in a generation that Hawaiians are being asked to decide an open Senate seat. The seat opened up after Hawaii's 88-year-old junior senator, Daniel Akaka, first elected in 1990, announced his retirement last year. Hawaii's senior senator, 88-year-old Daniel Inouye, has been in office since 1963—the longest of any other member of the current Senate—and is also a Democrat.
Whoever wins on Nov. 6 will make history in the Aloha State. Hawaii will have its first woman senator, and if Ms. Hirono wins the nation will also get its first Buddhist and Asian-American woman.
Ms. Hirono, who turned 65 on Saturday, immigrated to Hawaii as a child with her family from Japan. She earned a law degree from Georgetown University and in 1994 was elected Hawaii's lieutenant governor. Ms. Lingle, 59, moved to Hawaii as a young adult from the U.S. mainland and worked in public relations and newspapers before being elected mayor of Maui County and was elected the state's first woman and first Republican governor in 40 years in 2002. Hawaii became the 50th state in 1959.
In that election, Ms. Lingle narrowly defeated Ms. Hirono, who went on to win a seat in Congress in 2006, and is now serving her third term. In an interview, she said that 2002 loss steeled her for future campaigns.
"I did learn a lot from that race," Ms. Hirono said by telephone on a recent break from duties on Capitol Hill. "I have won all the other races since."
Political observers say the political winds are far more favorable to Ms. Hirono than a decade ago. "Hirono wasn't as strong then, and the (Hawaii) Republican Party is weaker now," said Neal Milner, professor emeritus of political science at the University of Hawaii. "This time Lingle is running for Senate against an established Democrat who has established Democratic support."
Ms. Hirono's immigrant heritage is also seen as a plus in courting many voters who not only are Democrats but have immigrant roots like herself. Democratic voter Bennette Misalucha, for instance, says Ms. Hirono's life story is similar to her own of having immigrated to Hawaii from the Philippines.
"At the end of the day, I will vote for Mazie because of who she is and what she can do for me," says Ms. Misalucha, 52, a government relations consultant on the island of Oahu and past president of the Filipino Chamber of Commerce of Hawaii.
Ms. Lingle, however, attacks her opponent as rigidly partisan at a time when many Americans are clamoring for more bipartisanship. "There has to be compromise," Ms. Lingle said in an interview at a Sept. 18 campaign rally in this village on Oahu's North Shore. "There is no other way forward for this country."
Ms. Hirono responds that the former governor would become a tool of the national Republican Party, and potentially help push the Senate out of the hands of Democrats—to the detriment of Mr. Obama's agenda, should he be re-elected. "People in Hawaii are really concerned in this race with who will really work closely with Barack Obama," Ms. Hirono said.
At the rally outside an elementary school, the former governor addressed Mr. Obama's popularity in Hawaii head-on, while acknowledging she planned to follow her party in voting for Republican Mitt Romney for president. "I am not going to work for Obama or Romney," Ms. Lingle told a crowd of about 500—many of them Mormon Republicans in this conservative-leaning town—as they ate chicken and rice at outdoor tables. "I'm going to work for the people of Hawaii."
That kind of talk helped win over voters like 76-year-old Emma Ernestberg, an Obama supporter who said that while "I like Mazie," she plans to vote for the former governor. "If a person is chosen by the people," said Ms. Ernestberg, wearing an American flag jacket, "it shouldn't matter what party they are."