The Democratic U.S. Senate race between Sen. Daniel Akaka and Rep. Ed Case has been one of the most polarized political contests in local history, with an unusually high number of voters choosing sides early.

The many made-up minds leave the candidates mostly courting a relatively small — but vital — pool of undecided voters in their one-and-only debate at 7:30 p.m. tomorrow on PBS Hawai'i.

Reaching these voters poses distinctly different tests for the two candidates, with the greater burden resting on Case — the challenger who has agitated relentlessly for a debate.

Akaka has never been an eloquent debater, and nobody really expects that of him.

For him, the evening will be a success if he simply shows that he's not afraid to face his challenger and demonstrates that, at 81, he's still capable of thinking on his feet under pressure.

Akaka has stayed in the background for much of the campaign, letting his staff and fellow senators such as Daniel Inouye, Barack Obama and John Kerry do his talking for him.

The most many voters have heard directly from Akaka is, "I'm Sen. Daniel K. Akaka and I approved this message."

The debate is his chance to stand front and center and show he can still hold his own.

For Case, 53, the debate presents a weightier challenge: He needs to answer the "Where's the beef?" question from an old hamburger commercial that Walter Mondale famously used to accuse opponent Gary Hart of having more style than substance.

His campaign could be in serious trouble If he devotes himself to trying to rattle his elderly opponent instead of staking out clear ground on key issues and getting specific about what he would bring to the job.

So far, the Akaka campaign has consistently beaten Case to the punch in defining the issues — and that includes defining Case's positions as well as Akaka's on their differences such as the war in Iraq, Republican tax cuts and the Patriot Act.

Case has mostly pressed broad calls for a generational change in Hawai'i's congressional delegation and a more moderate and bipartisan approach to national policy-making.

But even those who follow the campaign closely find it difficult to put a finger on exactly what these themes mean in concrete terms.

Case's most recent campaign mailer is cartoonish in the distinctions it draws between him and Akaka.

Akaka is "past," Case is "future." Akaka is "far left," Case is "moderate." Akaka is "party first," Case is "country first." Akaka is "controlled," Case is "independent." Akaka is "ineffective," Case is "leadership." Akaka is "for the few," Case is "for all."

The simplistic characterizations provide voters little useful information — and as a practical matter, attempts to paint the courtly and grandfatherly Akaka as a radical extremist aren't going to fly with most voters.

Case would have gotten more mileage using the piece to clarify his differences with Akaka on Iraq, where Akaka has won major points among many Democrats for his consistent opposition to the war and calls for an early withdrawal of U.S. troops.

Wavering Democrats want to know if Case differs with Akaka only on the timing of a withdrawal, or if he buys into President Bush's "stay the course" policy.

When he does address substantive policy, Case is often vague.

His "megachallenges" point out general goals that almost anybody would agree with — balancing the budget, securing the homeland, leading the world, growing the economy, protecting the earth — but he's been short on the details where the devil resides.

The debate is Case's best chance to put flesh on these bones and define himself instead of letting the Akaka camp do it for him.

David Shapiro, a veteran Hawai'i journalist, can be reached by e-mail at dave@volcanicash.net. Read his daily blog at blogs.honoluluadvertiser.com.