– In every statewide election of the past decade, as Prince William County has gone, so has gone the commonwealth of Virginia.

That goes a long way to explaining why President Obama staged one of the largest rallies of the year at an outdoor amphitheater here on a Saturday night, following former president Bill Clinton and musician Dave Matthews onstage and greeting a thunderous crowd of 24,000 despite the brisk November temperature, which dipped toward 40 degrees by the time Obama took the stage around 11 p.m.

It was Obama’s fourth campaign appearance of the day, and he again delivered a closing argument in which he asked for four more years to continue the changes he began in 2008. Starting to lose his voice with just three days remaining until Election Day, the president was at turns feisty and reflective, pointedly criticizing Republican challenger Mitt Romney and praising his own campaign organization.

Recalling a backstage moment with his senior adviser, David Plouffe, whom Obama called “mastermind” of campaign organizing, the president said the two agreed that, “as the campaign goes on, we’ve become less relevant. I’m just sort of a prop.”

The comment quickly attracted considerable attention on Twitter, where Romney advisers seized on it. Spokesman Ryan Williams referred to the president as the “incredible shrinking candidate,” and Romney senior adviser Kevin Madden tweeted: “Huh? Wha? #closing argument.”

The president did not pull his punches with Romney, repeating a line from Clinton, who said the Republican has “brass” for claiming in his own election windup that he is the candidate for change this year. Obama also reminded his supporters that even with so little time left, work remains. The campaign says it built an even larger grass-roots organization in Virginia than in 2008; organizers said that volunteers knocked on 500,000 doors across the commonwealth Saturday – more than in any other state in the country — and made 460,000 calls in the state.

“Virginia, in three days, you’ve got a choice,” the president said. “And even if you’ve already made the choice, you’ve got to talk to folks who haven’t.”

Polls continue to show a neck-and-neck race between Obama and Romney nationally and in Virginia. In the Old Dominion, Obama’s chances rest on spurring at least the same level of historic turnout that he attracted four years ago, particularly among African American, Latino and female voters. Romney is hoping to win over many of the exurban Democrats who came out for Obama last time, and to run up support in conservative strongholds, such as southside and southwest Virginia.

Clinton has lost his voice campaigning for Obama – “I’ve given my voice in service of the president,” he joked – but that didn’t stop the crowd from cheering cacophonously when he took the stage, nor stop him from relishing his job of introducing the president.

Slamming Romney’s unwillingness to take a stand on the Lily Ledbetter Fair Pay Act, Clinton said: “Folks, you’re going to have a lot harder decisions that this.”

And going after Romney’s accusation that Chrysler, which is owned by an Italian company, used auto bailout funds to send jobs to China, Clinton said: “Now he’s going after the Italians. If the Irish are next, I’m toast.”