Republican candidate George Allen speaks during a Senatorial debate for the Virginia U.S. Senate seat with Democratic candidate Tim Kaine on Thursday, Sept. 20, 2012 in McLean, Va. (Evan Vucci/AP)

Turn on a TV in Virginia and there’s one message that Republicans want voters to hear: Timothy M. Kaine loves taxes.

With just weeks before the commonwealth’s marquee U.S. Senate contest, Kaine’s opponent, fellow former governor George Allen (R), and conservative groups are shifting their strategy to increasingly link the Democrat to tax increases. They are betting millions of dollars in advertising that the issue is Kaine’s biggest vulnerability.

Republicans more frequently attacked Kaine earlier in the race for his ties to President Obama, and connected him to controversial administration policies such as health-care reform and the economic stimulus package. With Obama running competitively in Virginia against Mitt Romney (R), some observers say it is obvious why Republicans would stop twinning Kaine with the president.

“If you make your Senate race about Obama and Obama wins the state, that’s an ‘uh-oh moment’ that generally doesn’t end well,” said Chris LaCivita, a veteran Virginia Republican consultant.

Despite the campaign money pouring into the Virginia contest — including $10.3 million from related GOP groups American Crossroads and Crossroads GPS — it’s unclear whether the Republican message is working. Eight of the last nine publicly released polls show Kaine in the lead (although some were within the margin of error), and there’s little evidence that Kaine’s personal popularity is eroding.

A Washington Post poll released last month found 54 percent of registered voters had a favorable impression of Kaine, up from 41 percent in May. Other surveys have ranked his favorability in the 40s, but none have suggested that the number is dropping.

The Post poll also found just 5 percent of voters said taxes was the most important issue in the Senate race, while 29 percent said the economy and 10 percent cited jobs and unemployment.

But Republicans say they are focusing on taxes because they can link Kaine’s campaign proposals to his tenure in Richmond — an issue that may come up at a second candidates debate Monday night.

“A lot of it has to do with a significant portion of his record as governor,” said Nate Hodson, a Crossroads spokesman. “What would lead him to behave any differently in the U.S. Senate?”

One recent Crossroads ad accused Kaine of wanting to raise taxes because he’s “addicted” to spending. Other Crossroads spots, nominally about energy plans or education cuts, go back to the allegation that Kaine is a serial tax-raiser. Last month, anonymous — and possibly illegal — text messages sent to some Virginians accused Kaine of backing “a radical new tax plan.”

The Allen campaign, which has targeted much of its advertising on female voters with positive messages about the Republican, jumped on the tax issue after Kaine said at a Sept. 20 debate in McLean that he was “open to a proposal that has some minimum tax level for everyone.”

Within days, Allen was up with an ad accusing Kaine of supporting “raising taxes on everyone,” though Kaine had only said that he was willing to discuss a minimum rate — not that he endorsed it — that would raise taxes only for those not meeting the new threshold.

“Having exhausted other lines of attack, George Allen and his allies are growing increasingly desperate by knowingly promoting false claims on television and via anonymous text messages that misrepresent Tim Kaine’s proposals,” said Kaine spokeswoman Brandi Hoffine. (Allen has denied any role in the text messages.)

The Kaine campaign, which cited data from the Tax Foundation to show that the overall tax burden was lower under Kaine’s governorship than Allen’s, thinks the tax issue can actually be more of a weakness for Allen.

Allen favors extending all the Bush-era tax cuts, even though national surveys have shown majorities of Americans — 65 percent in an August Washington Post/Kaiser poll — favor Obama’s proposal to let the cuts expire on incomes over $250,000. Kaine supports letting taxes go up on incomes over $500,000.

Allen wants to close the deficit without raising any taxes and while averting planned defense cuts, a strategy that Democrats and some experts find implausible. And while Allen has promoted the idea of a flatter tax code with fewer deductions, he has not specified the rate or which deductions he would eliminate.

Obama, meanwhile, gets mentioned in ads far less often now than at the start of the Senate contest. In last month’s Post poll, 50 percent of registered voters said Obama would not be a factor in their Senate race vote, while 28 percent said they’d use their Senate vote to express support for the president and 20 percent to express opposition.

Linking Kaine and Obama made sense early on, LaCivita said, but “clearly it’s not the straw that’s going to break the camel’s back.”