The Democratic primary race for one of Hawaii’s most powerful political posts, a seat in the U.S. Senate, has national implications for the closely divided chamber.

U.S. Rep. Mazie Hirono is among the most liberal members of the U.S. House. Her primary opponent, former U.S. Rep. Ed Case, built a more moderate record during his three House terms. Their differences, in both policy and style, are significant. Hawaii Democrats will need to make a thoughtful, fully informed choice about whom to advance to the general election.

Unfortunately, Hirono has chosen to make it difficult for voters to weigh their options. Thus far, she is restricting her appearances with Case mainly to a handful of debates at small, private venues and a televised forum on PBS Hawaii. She has not accepted invitations from any of the major news media outlets to debate Case in front of the largest Hawaii audience possible. Perhaps Hirono will at some point closer to the election.

She certainly should.

Voters should be provided ample opportunity to see the candidates side by side in a robust exchange of ideas, in order to weigh two clearly experienced but significantly different candidates on the issues.

Progressive Punch, which rates members of Congress, has ranked Hirono, completing her third term, as the sixth most liberal among the 435 House members.

Case recalled that his National Journal rating was among the 38th most liberal members by the National Journal; he noted that the National Journal rates Sen. Daniel Inouye as the 36th most liberal among the 100 senators.

During his years in Congress, Case was a member of the Blue Dog Coalition, composed of Democratic Party members of the House who identify themselves as moderates who are considered to be relatively conservative on fiscal issues.

During her three terms in office, Hirono has predictably voted as a liberal Democrat. Her politics are progressive and she has won the support of liberal political groups ranging from the AFL-CIO to Emily’s List.

Hawaii News Now and the Star-Advertiser have offered Hirono and Case a statewide TV debate, as have KITV with Civil Beat and KHON.

Instead, Hirono has agreed to appear with Case in forums before Oahu County Democrats, the Hawaii Lodging and Tourism Association and PBS Hawaii host Dan Boylan, and debates hosted by the Maui AARP and Hawaii Public Radio in May and early June, two months before the Aug. 11 primary.

Hirono’s insistence on controlled public appearances and TV commercials are perhaps a reflection of a front-runner playing it safe. She leads in the public opinion polls. Her campaign has raised $2.5 million, mostly from organized labor and other liberal interest groups, according to the Center for Responsive Politics, while Case has raised little more than $600,000.

It may be a political strategy, but it’s not one that best serves the public interest.

Of course, given his lack of money, it’s in Case’s best interest to get as much free air time as possible. So making an issue of Hirono’s reluctance to debate him — on his terms — is also a political strategy, if not one that’s useful as a basis to judge either candidate. His question, "What’s she afraid of?" is more rhetorical than substantive.

Even so, Hirono should answer that question with more full-throated debates with her opponent.

The future of the U.S. Senate is up for grabs; this race has garnered national attention as one of the most important in the country. Let the debates begin.