Unity08, the post-political-party campaign for the presidency, announced itself this summer with the assertion that the current polarized atmosphere was repugnant to voters, who quietly and desperately craved moderation.

It’s such a cheery idea that anyone would be crazy not to support it, though it pretends the raging success of the conservative Republican majority in Washington over a dozen years was an oddity rather than an institution. And it must have been made uncomfortable by the Senate Democratic primary in Connecticut recently, where an incumbent moderate got thumped by a friendly lefty newcomer.

Columnist John Mercurio in the National Journal recently looked at primaries around the country and found bipartisanship – Republicans and Democrats were united in voting farther away from the middle than they have previously. For instance, in Michigan, Mr. Mercurio writes, conservative minister Tim Walberg beat incumbent GOP Rep. Joe Schwarz, “who Walberg claimed was too moderate on taxes and social issues like abortion rights and gay marriage.”

In Colorado, a moderate Republican backed by retiring Rep. Joel Hefley was beaten by conservative state Sen. Doug Lamborn, who accused his opponent, Jeff Crank, of supporting the “radical homosexual lobby.” Democrats who have made it to the general election in Senate races are also unexpectedly liberal, says Mr. Mercurio – Rep. Sherrod Brown in Ohio, state Sen. Jon Tester in Montana and state Auditor Claire McCaskill in Missouri. Toss in the loss by Sen. Joe Lieberman in Connecticut and Unity08, which wants to blend Republicans, Democrats and independents and yield a multi-party presidential campaign, has its hands full.

This is what moderates hope: If people better understood the details of policy, if they honestly sought fair compromise, they would discover that they and their political opponents shared basic human values that allowed them to find a middle ground on the means to express those values. Thoughtful and broadly supported legislation would be passed and the nation would be a finer place.

This is what voters remember: 15 seconds on why one candidate is good and the other is a waffling ninny, which they already suspected anyhow.

Even as voters are not especially far apart – polls show the cultural divide on values issues not nearly as broad as candidates’ platforms suggest – a clear, succinct message is persuasive and such a message is always easier from the extreme right or left, especially if it is in reaction to a statement from the other extreme.

Unity08, or any group that wants to overcome extremism in politics, faces a system from the way district boundaries are drawn to the voting patterns in party primaries that rewards that simple message. If this summer’s trend holds, the people most supportive of the Unity08 idea will be those who don’t follow politics – and they don’t vote.