Pennsylvania, where the Democratic campaign heads on April 22 for a dramatic and possibly decisive showdown, is another must-win state for .
But it is also a should-win state.
Like neighboring Ohio, where Clinton won 54 percent to 's 44 percent, Pennsylvania's population is older and whiter than the rest of the nation. Its residents make less money than the national average, and are less well-educated. The issues that rank high on their list of priorities - like health care and the economy - are the ones on which Clinton tends to draw the most support.
And just as in Ohio, much of the state's political establishment is aligned with Clinton, led by a popular Democratic governor who's pulling out all the stops on her behalf.
"The voters in this state are more typical of the kinds of voters she wins in the exit polls," said Terry Madonna, the director of the Franklin & Marshall College Poll. "In Pennsylvania, the issue configuration and the demographics are nearly perfect for her."
Clinton's advantages aren't just rooted in demographics. Her late father, Hugh Rodham, a graduate of Penn State University, was born and buried in Scranton, an old coal town in northeastern Pennsylvania. As a child, she vacationed at the family cabin in Lake Winola.
Her husband, Bill Clinton, also spent considerable time in Pennsylvania, twice carrying the state despite his rocky relationship with popular former Democratic Gov. Robert P. Casey.
"The Clintons have been coming here for 16 years whether as candidates or as president," said Larry Ceisler, a Democratic political analyst. "Pennsylvanians are very familiar with the Clintons and the Clintons are very familiar with Pennsylvania. Pennsylvania has given them lots of votes and money."
The most important connection of all, however, may be to Governor Ed Rendell, an earthy, old-school pol whose prodigious fundraising and retail politicking skills obscure an interest in policy that mirrors Hillary Clinton's.
Rendell, a former Philadelphia mayor and Democratic National Committee chairman, brings more to the Clinton campaign than just a standard endorsement. His fundraising operation is unmatched among Democratic governors and his popularity is rooted in Philadelphia and its populous suburbs, the regional lynchpin to any statewide victory.
"The Rendell factor is hugely important. There's arguably no stronger Democratic leader in America," said T.J. Rooney, the state Democratic party chairman and a Clinton supporter. "He has tremendous influence. He's a Democratic governor re-elected with 60 percent. He's a politically potent force and when it comes to fundraising, few can rival him."
Yet it is in Philadelphia, the city that elected Rendell to two terms as mayor, and its suburbs, which gave him landslide margins in his 2006 re-election campaign, where observers expect Obama will draw the bulk of his support.
Though Clinton has the support of Mayor Michael Nutter, an African-American who was elected in 2007, Philadelphia's heavy concentration of African-Americans, liberals and college students lead most observers to view it as Obama Country.
Madonna says about 15 percent of the statewide Democratic primary vote will be cast by black voters, with the majority of it coming from Philadelphia, by far the state's largest city. The Hispanic vote is considerably smaller, closer to three percent, and distinctly different than in California and Texas since Pennsylvania's Hispanics tend to be of Puerto Rican heritage.
The prosperous white suburbs outside the state's largest city also offer fertile ground for Obama. Ceisler, who recently attended an Obama fundraising event at a home located in an affluent Main Line suburb, says he was stunned by the turnout.
"They raised $180,000 in a house, with no candidate there," he said. "I've never seen anything like it."
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"He's gaining traction here," said state Rep. Josh Shapiro of suburban Montgomery County, an Obama supporter. "The Democratic establishment is with Senator Clinton but elections are won, particularly in southeast Pennsylvania, not by machine-style politics but by connecting directly with voters, which Senator Obama does very well."
Shapiro notes that the long period of time between the March 4 primaries and Pennsylvania's April 22 contest - the longest extended stretch of time without any major primaries this year - affords Obama plenty of time to gain ground on Clinton.
"Senator Obama has six weeks to run a campaign here, as opposed to Ohio where he had only two or three weeks," said Shapiro. "The results in Ohio will have little bearing, if any, on Pennsylvania."
Attitudes toward cultural issues represent one big difference between the Philadelphia metropolitan area and the rest of the state. Support for gun control and abortion rights is considerably weaker outside of southeastern Pennsylvania, which explains why, unlike most other Democratic-leaning Northeastern and Mid-Atlantic states, Pennsylvania remains a place where a pro-gun and pro-life Democrat can still win the party nomination for statewide office, as evidenced by the 2006 U.S. Senate victory by Bob Casey, the son of the former governor.
Many of those more culturally conservative voters can be found on the other end of the state, in the Pittsburgh area and in southwestern Pennsylvania.
In that part of the state, Obama begins at a slight disadvantage. The African-American population is considerably smaller in Pittsburgh than in Philadelphia, and western Pennsylvania is heavily populated by white ethnic, Catholic and blue collar voters with whom Clinton has proved popular.
"If the election were held tomorrow in western Pennsylvania, the numbers would be similar to Ohio," said Jim Burn, Pittsburgh's Allegheny County Democratic party chairman. "But the Obama campaign has 6 weeks to chip away here. And there's a lot of movement on the Obama side. The Obama folks have an outstanding field game out here now so those numbers are fluid and will in all likelihood change."
Burn noted that on February 10, county Democrats held a non-binding straw poll among the 1,400 party committeemen and women. Clinton won by a 2-1 margin.
In western Pennsylvania, said Burn, an Allegheny County Councilmember, "the economy and health care are going to be huge because there's a large demographic of senior citizens and families out here who are struggling."
By Charles Mahtesian