PHILADELPHIA, Pennsylvania (CNN) -- The ground war matters most now, and a little humor never hurts before a few hours of trudging through neighborhoods, looking for votes.
So in a pep talk to Sen. Barack Obama's campaign volunteers, Gov. Ed Rendell frames the stakes with the tongue-in-cheek approach.
"Gov. [Sarah] Palin and Sen. [John] McCain have been living in Pennsylvania the last few weeks," Rendell said. "I am going to start charging them income tax."
Philadelphia's African-American population is Obama's base, and high urban turnout is critical to giving him a cushion to offset more conservative areas elsewhere in the state. But pockets of the city that are predominantly white also are critical; if the race statewide is close, how Obama fares among these voters could make a significant difference.
So Pat Wisch enthusiastically led her team through its ritual of checking voter registration lists, and heading off to knock on the next door or -- more often than not, on some streets -- to ring the call box to a loft apartment.
Or just corral a passerby. One Wisch exchange played out this way:
"I was wondering if you have decided who you are going to support in the election on Tuesday," Wisch said.
"I have, yes."
"Are you willing to share that?"
With a laugh: "Yes, I am a supporter of Obama."
Down the street a bit, Wisch buzzed an undecided voter who had heard from another Obama volunteer just minutes earlier.
"Yeah, you guys just called me, I just had this conversation," the man said.
"Well, it is Obama I hope?" Wisch asked.
"I haven't really decided," he responded.
Undecided voters worry camp Obama most at this point, especially in heavily Democratic neighborhoods and precincts. The concern is that if a voter is undecided at this late stage, perhaps race is an issue, though Wisch says she worries much more about the race factor elsewhere in the state. Watch the state's two senators talk about race, other election issues »
"I am not so sure about the small towns where, um, people have a difficult time with the race issue," she said. "I understand people's belief systems and how they have been raised. For me, though, the thought of electing a man of color is thrilling."
The scope of the ground operation is stunning. In Pennsylvania, there are more than 500 paid Obama campaign staffers and thousands of volunteers. At stake for the campaign: capturing the state's 21 Electoral College votes.
It helps to have friends as well. There are about 4,000 union volunteers for the final push in Philadelphia alone -- and about 15,000 labor foot soldiers for the statewide effort, many brought in from neighboring states where the campaign is not as competitive.
In CNN's Pennsylvania poll of polls -- released Sunday -- Obama leads McCain by 8 points (51 to 43 percent). The poll of polls does not have a margin of error. Watch CNN's Bill Schneider break down the polls »
The McCain campaign is wasting no time in reaching out to Democratic voters in the state.
"Well thank you. Well listen -- you know what, my dad was in the union for a long time."
Those words come not from a Democratic office but from a McCain-Palin phone bank that is part of an aggressive effort to sway disgruntled and more conservative Democrats.
The smaller McCain ground army has 100 paid staffers in Pennsylvania, and roughly 15,000 volunteers, among them voters of Sen. Hillary Clinton's Democratic primary campaign, like Joyce Levy, who say they can't back the Democrat who won.
"Barack Obama has a very thin résumé," Levy said in an interview. "I think he is not qualified to be president."
Camp McCain has "Democrats for McCain" efforts in many states and says the Pennsylvania chapter is among its largest. More than 1,000 members were part of outreach efforts in Pennsylvania this final weekend, though the campaign says a good number of them were from other states but came to Pennsylvania because of the do-or-die stakes for McCain. Watch McCain make his pitch to Pennsylvania voters »
Eighteen-year-old Christopher Carroll was initially a Clinton backer, and is now proof not all first-time voters are in the Obama column.
"I believe he stole the election at the convention," Carroll said of Obama. "So really being for John McCain is a protest vote."
Carroll concedes he is outnumbered at school these days.
"We did a straw poll in the school the other day, and it was 96 percent for Barack Obama and 4 percent for John McCain," he said.
The statewide polls aren't anywhere near that bleak. But McCain is down, and he's hoping disgruntled Democrats like Levy and Carroll help him deliver what would be a stunning upset in a state that last voted Republican for president 20 years ago.
CNN political producer Ed Hornick contributed to this report.