U.S. Rep. Mazie Hirono has a dominant hold in the Demo­cratic primary for U.S. Senate, a new Hawaii Poll shows, opening an early double-digit gap over former Congressman Ed Case.

Hirono tops Case 56 percent to 36 percent, a lead driven by overwhelming support on the neighbor islands and from traditional Demo­crats and union workers who are among the most likely to vote in the August primary. Case’s only advantage is among independents and Republicans, part of the reason why he has appealed to all voters to participate in the primary.

Voters strongly prefer either Hirono or Case over former Gov. Linda Lingle, a Republican, in the November general election. The poll found that both Demo­crats have identical double-digit cushions over Lingle.

The Hawaii Poll offers a snapshot of the Senate campaign six months before the primary to replace retiring U.S. Sen. Daniel Akaka, D-Hawaii, just as the candidates and interest groups begin television advertisements and other direct outreach to influence voters.

Joseph Mrasek, a public school teacher who lives in Kula on Maui, said he appreciated that Hirono, as lieutenant governor, stood with teachers during a 2001 strike. He also said he believes Hirono would be more loyal to Hawaii-born President Barack Obama than Case, who is known for his independence.

"I can appreciate it sometimes, but given the difficulty with the cooperation from the other side of the aisle, I don’t think the Demo­cratic Party needs any more Demo­crat-in-name-only kind of people there," he said.

Jack Munechika, an electrical engineer who lives in Mililani, said he thinks Hirono would have a better relationship with U.S. Sen. Daniel Ino­uye, D-Hawaii, and others in the state’s congressional delegation. "Her experience," he said of the reason he prefers Hirono. "I like Case, too, but it’s just that he’s trying to jump too fast, yeah?"

Many of Case’s supporters respect his independence and consider him a departure from establishment Demo­crats who have controlled the majority party. But others who like Case have doubts about Hirono and her ability to defeat Lingle.

"Personality-wise, I prefer Ed Case," said Summer Uwono, an accountant who lives in McCully and who has difficulty believing in Hirono.

The Hawaii Poll was conducted by Ward Research Inc. for the Star-Advertiser and Hawaii News Now from Jan. 26 to Feb. 5. The telephone survey on the Senate primary involved 599 registered voters statewide and had a margin of error of 4 percentage points. The portions of the survey related to the hypothetical general election matchups for Senate and the favorability ratings of the candidates involved 771 registered voters statewide, with a margin of error of 3.5 percentage points.

"At this point she’s positioned quite well in the primary," Rebecca Ward, president of Ward Research, said of Hirono.

Ward said that, as in previous primary campaigns, Case may again have difficulty because he is strongest among independents and Republicans.

"But against Democrats and those likely to vote in a Demo­cratic primary, he just has a tough way to go," she said.

Ward said voter perceptions about Lingle are rooted from the time she left office in 2010 after unpopular state budget cuts and teacher furloughs.

"She still has the issues and the baggage that she left office with, which caused her approval rating to fall so far," she said, adding that she expects the gap between Lingle and the Demo­crats to narrow in the coming months.

John Hart, a communication professor at Hawaii Pacific University, said the Hawaii Poll has a substantially different result from another survey on the Senate race in January. An automated poll taken by the online news site Civil Beat and the Merriman River Group showed Case and Hirono essentially deadlocked, with Case up 41 percent to 39 percent, within the poll’s 2.7-percentage-point margin of error.

"We’re in an extremely fluid situation given that we’re seeing a variety of polls with very different data results," he said.

The Hawaii Poll found that Hirono and Case are much closer on Oahu — 50 percent to 41 percent — than on the neighbor islands — 69 percent to 25 percent. Both Demo­crats have represented the neighbor islands in the 2nd Congressional District. Many political analysts had thought that population growth on the neighbor islands, particularly on Hawaii island and Maui, would gradually change the political dynamics, but the neighbor islands have remained deep blue territory for traditional Demo­crats in recent elections.

Hirono dominates Case among traditional Demo­crats, 64 percent to 31 percent, and in union households, 63 percent to 31 percent — voters who have proved more likely to participate in the party’s primaries. The congresswoman also fares well among women, Japanese-Americans, Hawaiians, young people and low-income voters.

Case has a healthy edge over Hirono among independents — 47 percent to 38 percent — and Republicans — 60 percent to 32 percent. Case’s strategy in previous campaigns has been to urge independents and Republicans to vote in the Demo­cratic primary, since the primary is open to all voters, an appeal complicated this year because of Lingle.

Lingle, who faces attorney and former state lawmaker John Carroll in the GOP primary, is expected to win her primary easily. However, she will likely make some effort to woo independents and keep moderate Republicans from straying into the Demo­cratic primary.

Lingle, the poll found, trails both Hirono and Case by 20-point margins. But the former governor has an advantage over the Demo­crats among independents — 57 percent to 39 percent over Hirono, and 53 percent to 38 percent over Case — a voting bloc she must rule to compete in November. Lingle needs to capture most independents and a share of moderate Demo­crats to win, a formula that will likely be influenced by how these voters perceive President Obama.

The president’s job approval rating in Hawaii is at 69 percent, according to the Hawaii Poll, down from 74 percent in May but still well above his 48 percent rating nationally by Gallup. Obama’s popularity would likely have to drop significantly in the islands to persuade enough independents and moderate Demo­crats to split their tickets and choose a Demo­cratic president and a Republican senator.

The Hawaii Poll also suggests that a pattern that played out during the 2002 governor’s race — when Lingle beat Hirono after Hirono overcame Case in the primary — is emerging again.

If Case were to lose in the primary, the poll indicates, his voters would prefer Lingle over Hirono 49 percent to 47 percent. If Hirono were to lose in the primary, her voters would favor Case over Lingle 71 percent to 21 percent.

Part of the explanation for Hirono’s early lead is that voters continue to give her high favorability ratings. Sixty-four percent of voters view her favorably — the highest among all candidates tested in the survey — compared with 53 percent for Case and 49 percent for Lingle.

"The people of Hawaii are looking for a senator who truly understands the struggles everyday families face, has the right approach to growing our economy and creating middle-class jobs, and will bring a Hawaii tradition of strong and cooperative and inclusive leadership to the U.S. Senate," Hirono said in an email. "It’s humbling to see these early signs of support, but I will never take that support for granted — because a stronger future for Hawaii is what’s at stake."

Case pointed to the disparate results of different polls.

"There’ve been some wildly different poll results over the past months. Another independent poll from just last week with twice the sample showed us leading Mazie in the primary and doing much better than her against Lingle in the general," he said in an email. "This election is very fluid with a long six months still until voters actually vote. We’re confident that, as voters compare Mazie and me on the strong effective leadership needed in D.C. and the issues that matter, like strengthening our economy, fixing Washington and doing the job over the next generation, our support will continue to grow."

Lingle, who described herself as the underdog, said the Demo­crats will get the most attention in the months leading up to the primary.

"We’re not where we hope to be on Election Day, but I am used to beginning every campaign as the underdog," she said in an email. "The general election is almost nine months away and because both Demo­crats have been running lots of television commercials in their very competitive primary, they are getting most of the attention. That will change after the primary election on Aug. 11.

"I do like our advantage among Independent voters since we believe they will be the deciding factor in the election."

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The most recent poll was conducted among 771 registered voters by telephone (land lines and cellphones) Jan. 26-Feb. 5 by Ward Research Inc. The margin of error is plus or minus 3.5 percentage points.  The 2011 poll was conducted May 4-10 among 614 registered voters by telephone (land lines and cellphones) by Ward Research. The margin of error is plus or minus 4.0 percentage points.