Republican George Allen on Tuesday attacked his Democratic rival in Virginia's U.S. Senate race, Tim Kaine, for suggesting that even the poorest Americans could pay income taxes, while Kaine sought to parlay his flexibility on taxes into a virtue.

Allen launched his latest attack in a blistering new ad that uses video of Kaine saying during last week's debate that he would "be open to a proposal that would have some minimum tax level for everyone."

"Tim Kaine's response to nearly every challenge is to raise taxes," said Mike Thomas, Allen's campaign manager. "Starting on his sixth day as governor, Tim Kaine tried to raise taxes by $4 billion while 100,000 Virginians lost their jobs. It should come as no surprise that Tim Kaine's plan in Washington is more of the same."

Kaine defended his debate performance during two appearances in Northern Virginia, including a stop in Fairfax at which he picked up the endorsement of the Virginia Professional Fire Fighters. Union President Michael Mohler lauded Kaine's willingness to go to Washington open to any ideas to fix the deficit, including tax increases and spending cuts.

Kaine was asked during the debate whether he would be open to a proposal to impose a minimum tax to cut the deficit. He said he would be, but later said he doesn't support imposing such a tax. He said he was demonstrating his willingness to hear all proposals when dealing with complex problems.

"I'm going to start always with my colleagues, Democrat and Republican, in a position of openness," Kaine said. "If you want them to consider your ideas, you have to be willing to be open to hearing theirs."

Kaine proposed reducing the federal budget deficit by letting Bush-era tax breaks expire for those earning $500,000 or more a year and by eliminating multibillion-dollar subsidies to oil companies. He isn't proposing a minimum tax.

Sen. Chris Coons, D-Del., who joined Kaine on the campaign trail in Arlington, backed Kaine's approach, saying neither party could negotiate in good faith unless it was willing to examine everything.

"I don't think anything should be off the table," Coons said.

Allen proposed reducing the deficit through spending cuts -- including the repeal of President Obama's health care reforms -- and by increasing domestic energy production. No tax increases are needed, he said.

Evan as Allen attacks Kaine for being open to tax increases, Kaine is using Allen's no-tax pledge to portray him as an obstructionist who would help extend the partisan gridlock that already prevents Congress from resolving critical issues.

"Before it's a question about taxes," Kaine said, "it's a question about what is blocking us from progress."