Updated

John Kerry's (search) presidential campaign on Thursday again challenged President Bush to one-on-one debates, saying the fiercely negative tone of the White House race has clouded the issues.

In a letter Thursday to Bush campaign chairman Marc Racicot (search), Kerry campaign chairwoman Jeanne Shaheen (search) said holding debates now would allow voters "the honest dialogue they deserve."

The Bush campaign did not take up the offer, with spokesman Scott Stanzel saying now was not the time for debates.

"We look forward to robust and spirited debates at an appropriate time, but Senator Kerry needs to finish the debate with himself," Stanzel said in criticizing the Democrat for waffling on positions.

Stanzel declined to say whether Bush's campaign would agree to early season debates in the future.

Kerry's campaign is pinpointing six battleground states to debate issues where it says the Bush administration has been unsuccessful: homeland security and veterans in Pennsylvania, education in Arizona, the environment in Washington state, jobs and the economy in Ohio, health care in Missouri, and equal opportunity in Florida.

Kerry challenged Bush to monthly debates in mid-March, saying then that "America shouldn't have to put up with eight months of sniping."

Since Kerry emerged as the presumptive Democratic nominee, both candidates have criticized each other, at times sharply, on everything from national security to taxes. Kerry's first negative television ad, released Thursday, claims Bush's economic policies have shipped U.S. jobs overseas.

Regardless of whether the candidates agree to an early debate, a series of presidential debates is still set for the fall, with an independent commission controlling the schedule.