About 9,000 people came out to hear the presidential contender. 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 the shivering crowd.
The weather was so miserable that Obama's rival, Republican John McCain, canceled a rally 50 miles north in Quakertown - hardly insignificant, given the dwindling campaign time.
Even Major League Baseball suspended the fifth game of the World Series in Philadelphia because of the same wet conditions Monday night, a first in the history of the baseball championship.
Gone were Obama's suit and tie. He wore jeans, sneakers and a waterproof raincoat. Still, shunning an umbrella, he got soaked. Obama later changed clothes before resuming his events.
McCain and Obama converged on Pennsylvania, a vote-rich state where Obama leads but McCain remains hopeful of a turnaround. Later, Obama was heading to Virginia, a longtime Republican state where he leads in polls.
Closing in on history, the front-running Obama has returned to broad, uplifting themes of change in hopes of ending the campaign in the most positive light.
The election is in one week.
Obama 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 the Democrat 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 except for one - Pennsylvania - where McCain is pushing hard to nab a win.
McCain and running mate Sarah Palin held a rally in Hershey, Pa., on Tuesday before going their separate ways - McCain to North Carolina, another contested state, while Palin stays in Pennsylvania. The event they scuttled in Quakertown was to be held at a baseball stadium.
Obama's rally was in the strategic Philadelphia suburb of Chester.
The small city is in Delaware County, a pivotal swing area of the state. Neighborhoods here range from economically depressed to working class to ritzy. Republicans hold an edge over Democrats in voter registration, and both campaigns are surging to get out the vote. Chester itself is predominantly black, but the broader county has a mostly white population.
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.
Obama was then heading to Virginia, which is offering up intense political interest this year. Obama is vying to become the first Democrat for president to win the state in 44 years.
The Illinois senator was staging a rally at James Madison University in Harrisonburg, an area which has posted one of Virginia's largest gains in voter registration this year.
At night, Obama will campaign in Norfolk, Va., a major military community. This will be Obama's ninth trip to Virginia since he clinched the Democratic Party's nomination in June.
McCain and Palin are campaigning aggressively in Virginia, too. The transformation of the Washington-savvy northern Virginia region, coupled with distaste for an unpopular president, no longer makes the commonwealth reflexively Republican.