With just a week to go before primary ballots are due, Seattle Mayor Greg Nickels' campaign is going negative on some of his top challengers.

Nickels yesterday tweaked his TV ad to juxtapose his "record of accomplishment" with the "empty sound bites" offered by his opponents. About half A good portion of the ad is consumed by footage of Nickels with President Obama.

Nickels also is starting robo-calls to voters attacking McGinn over his opposition to the deep-bore tunnel to replace the Alaskan Way Viaduct. McGinn has called the tunnel the "biggest tax increase in Seattle history." (McGinn favors tearing down the Viaduct and handling its traffic with road and transit improvements.)

But the Nickels campaign argues McGinn's plans would actually cost Seattle taxpayers more because the state legislature might withdraw more than $2 billion it has committed to the Viaduct project if McGinn is elected.

McGinn put out a statement this morning calling on Nickels to put the tunnel before voters, who overwhelmingly rejected a different tunnel plan in a 2007 advisory vote.

The Nickels campaign promises further efforts "to set the record straight" about other challengers (likely T-Mobile executive Joe Mallahan) in the coming week, before votes are counted on Aug. 18.