CHARLOTTESVILLE, Va. – Fighting to the end, President Obama on Friday devoted shrinking campaign time for one endangered Virginia Democrat, calling his bid a national test case of whether a person of integrity can win.

The president, bracing for an election beatdown in a prime electoral atmosphere for Republicans, plunged into a final weekend of campaigning, undeterred by the somber news of a new terrorist threat. He implored a young, raucous crowd in this college town to rally behind first-term Rep. Tom Perriello, who has loyally backed key parts of the president’s agenda.

“The reason I am here is because in this day and age, let’s face it, political courage is hard to come by,” Obama told thousands gathered outside on a crisp autumn night. “When you’re a first-term congressman, the easiest thing to do is make your decisions based on the polls. That’s not who Tom is.”

The stop was meant as more than a boost for Perriello, who is in a fierce election fight against Republican state Sen. Robert Hurt. The president also wanted to send a message to fellow Democrats and ambivalent supporters that he would stand with those who took tough votes on health care and stimulus spending — and his party should not run away from them.

Shadowing it all: fresh news of a weak economy still struggling to create jobs.

Predictions of a Republican blowout dogged the president and his party, as voters looked to take it out on incumbents over joblessness, bailouts and the toxic state of politics. Republicans were looking to recover from recent electoral lashings by claiming the House and making big gains in the Senate, governors’ mansions and state legislatures.

The tone of the day, meanwhile, had changed considerably before Obama arrived. From Washington, he declared that officials had uncovered a “credible terrorist threat” of U.S.-bound packages containing explosives aboard cargo jets.

Obama spokesman Robert Gibbs said the president’s weekend political travels would not be altered as the terror probe continues. Indeed, by the time of the evening rally, Obama had his sleeves rolled up in full-fledged campaign mode.

The White House has sought to win the expectations game, conceding the election will yield more “parity” between the parties in Washington, as Obama adviser David Axelrod put it, and pressuring to Republicans to show more leadership.

Obama, at the rally, challenged voters to defy cynical politics. “We say we want integrity from our elected officials,” Obama said. “But you know what, this is a test case right here, in Charlottesville. This man has integrity.”

In a nod to the pressures facing Perriello, the two acknowledged they don’t always agree. Perriello’s opponent, Hurt, said earlier in the day that Obama was coming to town to reward the congressman as a “loyal foot soldier.”

Obama set out on his final round of campaigning for Tuesday’s election as official tabulations showed more than 11.6 million voters had already cast ballots, including more than 2 million in California, 1.6 million in Florida and 1.2 million in Texas.

There also were high totals in other states where races were particularly intense, including nearly 675,000 in Colorado, where Sen. Michael Bennet is in a close contest with Republican challenger Ken Buck.