Republican Senate candidate George Allen on Thursday stood side by side with his party's presidential nominee in Virginia, looking to rally his base and appeal to a small but crucial number of Mitt Romney's supporters who plan to vote for Allen's Democratic opponent.

In their first appearance together since early September, Allen gave Romney a full-throated endorsement and pushed hard for Virginians to vote a straight Republican ticket on Tuesday. Speaking in Doswell, near the birthplace of legendary racehorse Secretariat, Allen implored Romney supporters to deliver a "Triple Crown victory" by casting a vote for him, Romney and House Majority Leader Eric Cantor, R-Va.

"The key to the winner's circle: Mitt Romney in the White House," Allen said.

Though the Senate race remains tight, polls consistently show Allen running behind Democrat Tim Kaine. The latest CBS News/New York Times/Quinnipiac University survey showed Democrat Tim Kaine leading Allen 50 percent to 46 percent.

Kaine for weeks has been performing better in Virginia polls than President Obama, in a clear indication that some voters planning to vote for Romney will split their ballot and vote for Kaine over Allen. The polls show 93 percent of Virginia Republicans backing Romney but just 87 percent supporting Allen. Kaine has the support of 95 percent of his fellow Democrats.

Nursing a narrow lead in the final days of the campaign, Kaine has shut down his attack ads and replaced them with a pair of spots that emphasize his commitment to working in a bipartisan manner in Washington.

While Allen was appearing with Romney on Thursday, Kaine was touring with Sen. Mark Warner, D-Va., at his side. Warner was part of a group of senators who tried unsuccessfully to draft a bipartisan budget deal last year, and he reassured voters that Kaine would work in the same bridge-building manner.

"My sense is an undecided person at this stage, they're probably most looking for who can go in and break gridlock, who can reach across the aisle," Kaine said during a Thursday morning stop in Alexandria. "It's just all about trying to persuade those last undecideds here."

Kaine and Warner on Friday will take the message of bipartisanship to southwestern and southern Virginia, reliably Republican turf in recent elections.

Allen, meanwhile, continues to assail Kaine, releasing a new ad bashing the Democrat's energy policies.

Allen reported borrowing $500,000 to fund his campaign and last-minute ad buys in key markets. His aides said the line of credit is intended only to help manage cash flow as they wait for credit card contributions to clear.

Allen cited his own bipartisan accomplishments as governor, comparing them to Romney's time as governor of Massachusetts dealing with a Democratic legislature. But Allen also riffed on ideological issues important to his core supporters.

"When we have Mitt Romney in the White House, we're going to have a president that will stop the [Environmental Protection Agency's] assault on coal," Allen said, "and he'll be saying yes to Virginia energy."