An already bitter battle for Virginia's open U.S. Senate seat got nastier Wednesday as Democrat Tim Kaine and Republican George Allen unveiled new television attack ads.

The two former governors vying to replace retiring Sen. Jim Webb, D-Va., struck a more negative tone than in previous, mostly biographical ads as candidates move past the conventions and prepare for their first debate Sept. 20.

Kaine is far more aggressive in attacking Allen than in his previous three ads. The new 30-second spot says Kaine balanced the budget as governor amid a fiscal crisis while Allen, who served in the Senate from 2001 to 2007, is part of a Congress that "helped turn a record surplus into a massive deficit."

Allen, meanwhile, looks forward, focusing on boosting domestic energy production and avoiding $500 billion in looming defense cuts backed by the Obama administration that promise to disproportionately impact military-centric Virginia.

It's a backhanded attack on Obama, an ally of Kaine, without mentioning either. Allen has recently focused on those pending Pentagon cuts, leaving Kaine scrambling to clarify that he has called for a new deal to avoid them.

Allen's campaign has set aside $5 million for the ad buy. Kaine reserved $4.5 million in fall airtime earlier this year.

Kaine speaks directly to voters in his ad, a move that his campaign said is necessary to humanize Kaine in the face of $10 million of negative ads from conservative organizations that have "demonized" the Democrat.

Outside groups, predominately conservative, have funneled more money into Virginia's Senate race than any other state's, according to the Center for Responsive Politics, a national tracker of campaign finance. The latest attack against Kaine came Tuesday from Crossroads GPS, a group headed by GOP strategist Karl Rove.

On the heels of Kaine's speech at the Democratic National Convention last week, it seemed like an opportune moment for the Rove group to once again link Kaine to Obama. But Crossroads GPS has avoided the comparison for now.

"Maybe they're wising up over there," said Kaine senior adviser Mo Elleithee, who noted that the race remains deadlocked after months of Obama-Kaine ads. "They're getting a really bad return on their investment. It hasn't moved the needle."

Elleithee added that he doesn't expect Kaine to get a bump from attending the convention. For his part, Allen hopes independents will appreciate that he avoided his party's partisan gathering in Tampa, Fla.

"Tim Kaine used his convention appearance to double down on his support for President Obama's failed economic policies that have hurt Virginia families and small businesses," Allen spokeswoman Emily Davis said. "Virginians see that leadership is setting priorities, and that's what George Allen will do for Virginia."