The BBC's Max Deveson talks to voters in central Pennsylvania, which could play a crucial role in Tuesday's primary, and finds support for the two Democratic candidates varying between town and country.
Pennsylvania has long been seen as a crucial electoral state
Rarely can the citizens of Harrisburg - the state capital of Pennsylvania - have experienced the political excitement that this year's Democratic primary has brought to the city.
On Saturday Barack Obama spoke to thousands of supporters from the steps of the State Capitol building.
"The crowd was very enthusiastic," said Tracey, a lawyer from Baltimore, Maryland, who had travelled to Harrisburg to see the Illinois senator speak.
"At one point, when Obama was talking about the lack of jobs in the state, someone shouted out, 'That's why we're so bitter'. Everyone laughed."
The heckler was referring to Mr Obama's recent controversial speech at a California fundraiser, in which he said that small-town Americans were "bitter" and "clinging" to guns and religion because of economic hardship.
Senator Obama has been forced to apologise for the remarks, which could hurt him in parts of Pennsylvania, according to one voter.
"It's the kind of thing that liberal intellectuals might say to one another without realising how it sounds," said Amy, a chemistry professor at Dickinson College in Carlisle, not far from Harrisburg.
Town v country?
But in Harrisburg itself, there is little sign the comment has damaged him.
Everybody here is really excited about the primary
Mary Cain Hershey resident and Clinton supporter
Senator Ted Kennedy emphasised the importance of the city's voters at an Obama rally on Sunday morning.
"This is the time, this is the moment. They're the chosen ones to make the difference. So it's really - in a very important way - in the hands of the people here in Harrisburg,¿ he told the BBC afterwards.
"Senator Obama is appealing to the American people for sacrifice and service, and they are responding in a positive way," he added, in an echo of his brother John's famous appeal to the American people to "ask what you can do for your country".
Pennsylvania Senator Casey, the other star attraction at the rally, focused on the ways in which he felt Mr Obama would be good for central Pennsylvania.
"This area has been hit pretty hard economically with job loss and job dislocation. What Barack Obama is offering is not just a set of policies - he is the one candidate who can deliver on the promise of change," he said.
"His track record on taking on special interests and his ability to inspire and unite people show that he can do that."
But on the road out of the city, the Obama posters begin to disappear and more signs of Hillary Clinton's strong support in Pennsylvania emerge.
Some 200,000 new voters have registered to vote in Pennsylvania
Harrisburg is right in the centre of Pennsylvania, half-way between the state's main population centres, Pittsburgh and Philadelphia.
James Carville, Bill Clinton's chief strategist, once described the state as "Philadelphia and Pittsburgh, with Alabama in between".
Central Pennsylvania certainly is more rural - and more conservative - than the big cities on either side.
Not far from Harrisburg is the town of Hershey - home to one of America's biggest chocolate manufacturers.
This industrial town has certainly been hit by the job losses that Mr Casey highlighted - Hershey Co cut 1,500 jobs in February 2007 when it moved some of its production to Mexico.
Hershey resident Mary Cain, a retiree, is a big Clinton supporter.
"I'm sticking with her," she said.
"Hillary has the experience of being in the White House with her husband in the 90s. As [Pennsylvania Governor] Ed Rendell says -what didn't you like about living in the 90s?"
"Obama's lack of experience worries me, but I will give him some credit - he's finally persuaded people to get involved in politics. Everyone here is really excited about the primary," she added.
Voters in Philadelphia voice their views on Barack Obama and Hillary Clinton
Leaving Harrisburg in the opposite direction, towards Gettysburg - site of Abraham Lincoln's famous battlefield address - uncovered yet more support for Senator Clinton.
Mayra, a resident of Etters, Pennsylvania, used to be a registered Republican but is now planning to vote for Mrs Clinton in Tuesday's primary.
"It's got a lot to do with the failures of the current president. I'm really worried about the economy, and I think that Hillary would be able to bring new leadership," she said.
"It would be great to have a woman president as well."
Polling suggests that the candidates are running neck-and-neck in central Pennsylvania, with Mrs Clinton holding on to a small lead state-wide.
Both candidates have been running negative adverts in the state, and harsh words have been exchanged.
But despite the friction and bad temper, this close-run race has generated unprecedented excitement.
Some 200,000 new voters have registered in Pennsylvania since January, 70% of them as Democrats.
And the winning candidate will be hoping to surf this tidal wave of enthusiasm all the way to victory in the general election.
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