It had to happen, really.

At Saturday's debate, the two major party candidates, former attorney general Jerry W. Kilgore (R) and Lt. Gov. Timothy M. Kaine (D), finally declared the primary difference between them to be their opposing views on the 2004 tax fight.

For six months, that issue had been not quite unspoken, but not exactly on the front burner. Kaine talked about it now and then, as did Kilgore. But they preferred to focus on abortion, gun control, capital punishment, transportation and education.

No matter how important those issues are, it was inevitable that the historic debate over taxes in 2004 would eventually become the defining issue of the 2005 campaign.

It was, after all, the defining fight of Gov. Mark R. Warner's tenure and an eruption of a years-long struggle within the Republican Party. The tax fight caused Virginia's longest budget stalemate.

By the end, Warner (D) had persuaded enough members of both parties to approve a tax increase designed to raise $1.5 billion over two years and a package of other tax changes that Warner said were necessary.

Kaine praised the effort. Kilgore tried to kill it.

At the debate, in the Greenbrier resort in West Virginia, Kaine made it clear that he will stake his campaign on the notion that the public thinks that he was right and that Kilgore was wrong.

"The key event of the Warner administration was the budget reform of 2004," Kaine said. "Democrats and Republicans alike came together. . . . Jerry, where were you in 2004?"

There have been few public polls to test whether Virginians think Kaine was right. But there is some evidence that they might think so. Warner's approval ratings are through the roof, an indication that the public isn't all that angry about the tax increases. And when the increases took effect last year, the public made nary a peep.

If Kilgore is worried that he's on the wrong side of public opinion, he didn't show it at Saturday morning's debate.

Again and again, he turned questions about "budget reform" into Republican-style answers about his opposition to taxes and his pledge not to increase them.

"Let me be clear: Raising taxes does not equal leadership," Kilgore said repeatedly.

If the 2004 tax session remains the central issue, it will pose challenges and risks for candidates.

For Kaine, focusing on what he calls "budget reform" runs the risk of playing to a traditionally Republican strength: a debate over taxes. Warner wisely avoided a referendum on his tax proposals because of the danger that they would be too easily misrepresented in 30-second ads and sound bites. That could happen to Kaine during the next three months.

Kilgore can bash the tax increases all he wants, but in doing so he risks alienating a public that very much seemed to want the improvements in services they made possible.

True, there's a big state surplus now, and that makes it easier to argue that the tax increases weren't necessary. But teachers, police officers and sheriff's and local officials -- who benefited from the tax increases -- will argue that he's wrong.

State Sen. H. Russell Potts Jr. (R-Winchester), an independent candidate for governor, is going one step further than Kaine. He's arguing that the 2004 tax increases were not only necessary, but that they didn't go far enough. That could earn him points from the 2004 tax proponents, but it could render him untouchable to the vast majority of voters who don't want even higher taxes.

A front-and-center debate over the tax session would put Warner in a box if he seeks national office. His main political accomplishment is the effort's success. If he argues its merits on behalf of Kaine, and then Kilgore wins, it could tarnish Warner's success.

Warner might not have a choice. If he leaves Kaine to make the argument, the legacy of the 2004 session could still be in trouble.