Targeting two key states, Obama stayed on the safe ground of lumping Republican rival John McCain with President Bush.
"This election, more than any other in my lifetime, represents a clear choice between the past and the future," the 47-year-old Democrat said, ribbing his 72-year-old opponent.
Dropping into the Shenandoah Valley, Obama spoke first to about 8,000 people who spilled onto a soccer field at James Madison University because the indoor site was too packed.
Inside, Obama found 12,000 more people, mostly students who were too excited to sit.
On a day when Republican grumbling about McCain grew and polls showed Obama maintaining his lead, the Illinois senator said he took nothing for granted. He went ahead with at an earlier outdoor rally in the Philadelphia suburbs despite a steady, chilling rain.
About 9,000 shivering people came out to hear him there. They stood in mud.
"I just want all of you to know that if we see this kind of dedication on Election Day, there is no way that we're not going to bring change to America," Obama told them all.
About 50 miles to the north, McCain postponed a rally because of similar weather.
McCain and Obama both converged on Pennsylvania, a vote-rich state where Obama leads but McCain remains hopeful of a turnaround. McCain is also trying to hang onto Virginia, which may well go for a Democrat for president for the first time in 44 years.
"No state is going to be more important than this state, right here, the Commonwealth of Virginia," Obama said on site. He was holding an evening rally in Norfolk, Va., too.
The day was marked by a spat between the Obama and McCain camps, over whether a McCain adviser suggested people would be worse off under a McCain health care plan.
Obama called it a "stunning bit of straight talk - an October surprise." The McCain domestic policy adviser, Douglas Holtz-Eakin, said Obama's team had deliberately taken his comment out of context. "This continues their disgraceful campaign," Holtz-Eakin said.
In Pennsylvania, at Widener University, Obama ditched his suit and tie for jeans, sneakers and a raincoat. Still, shunning an umbrella, he got soaked.
Obama later changed clothes before resuming his events.
The election is in one week. Obama has returned to broad, uplifting themes of change in hopes of ending the campaign in the most positive light.
He promised better days "if we're willing to reach deep down inside us, when times are tough, when it's cold, when it's raining, when it's hard - that's when we when stand up."
Gunning for the 270 electoral votes he needs to win the White House, Obama is almost exclusively targeting tossup red states, the label for the ones that trend Republican. Any one of them might tip him to victory. Combined, they could give him a dominant win.
Meanwhile, he can afford to spend little time at all defending Democratic blue states.
In Hershey, Pa., McCain and running mate Sarah Palin told an audience that they delight in fooling the pundits. "I'm not afraid of the fight, I'm ready for it," McCain said.
Obama's Pennsylvania rally was in the strategic Philadelphia suburb of Chester, an area that, like the state itself, could swing to either candidate.
The event was a cross-state bookend to Obama's appearance Monday in Pittsburgh, where he pledged to cut taxes for the middle class and help factory workers as much as company owners.
(Copyright 2008 by The Associated Press. All Rights Reserved.)