In eight years since Pennsylvanians last chose a new governor, the landscape of each major political party has shifted in ways that could have some impact on the May 18 primary.
The Democratic Party that picked Ed Rendell as its candidate in 2002 has grown by 550,000 members, to more than 4.3 million, and its center of gravity has tilted slightly toward the Philadelphia region. Its voters are a bit younger, a bit more liberal.
The Republican Party has changed in some opposite ways.
Its ranks have shrunk by 103,000 voters, to 3.1 million, and its geographic core has shifted slightly west, toward Pittsburgh. With a loss of many moderates, and a failure to attract many new voters, it has become older, more conservative.
These changes, though subtle, figure into the campaigns being mounted by each of four Democrats and two Republicans running to succeed Mr. Rendell, who after two terms in office cannot seek re-election.
With Philadelphia having experienced an 8 percent growth in Democratic registration -- an additional 74,000 voters -- state Sen. Anthony Hardy Williams sits in a stronger position to follow a strategy based mainly on gaining votes in his hometown. In the four-way race, a candidate could win the party's nomination with as little as 30 to 35 percent of the vote.
Democrat Joe Hoeffel, a Montgomery County commissioner, likewise may be helped by his party's growth in the Philadelphia suburbs. In his home county, which had a Republican majority in 2002, Democrats now boast an 82,000-voter edge over the GOP.
So say the latest registration figures, complete through April 19, the deadline for registering to vote in the primary.
The five-county Philadelphia area, which had 34.4 percent of all Democratic voters in the state in 2002, now has 36.6 percent, a gain of 284,000 voters, according to those figures.
At the other end of the state, the two Pittsburghers in the Democratic race -- Allegheny County Executive Dan Onorato and state Auditor General Jack Wagner -- must contend with significant erosion of their party's base in southwestern Pennsylvania.
In the May 2002 primary, 27.8 percent of all Democrats lived in a nine-county region of the southwest. Today, it's just 23.8 percent, a loss of 20,000 voters.
This is due in part to population loss -- but analysts say it is also the result of conservative Democrats' disenchantment with the liberal tone of the party's politics at the national level.
"Democrats in Western Pennsylvania were always more conservative," said Berwood A. Yost, director of the Center for Opinion Research at Franklin and Marshall College.
Mr. Onorato remains the favorite in the Democratic primary, analysts say, in part because he has been able -- with $6.7 million on hand this month -- to run extensive TV advertising across the state. Mr. Williams, too, has run ads.
Mr. Wagner, like Mr. Hoeffel, hasn't bought ads. But Mr. Wagner is counting on experience as a three-time statewide candidate to earn him enough votes in all 67 counties to eke out a win.
The Western Pennsylvania Democrats in the race, Mr. Wagner and Mr. Onorato, could have one equalizer when it comes to regional politics.
The thinning of their party's ranks in the Pittsburgh region could be partly offset by the historic tendency of Western voters to turn out in higher percentages than their Eastern Pennsylvania counterparts.
Western voters are generally older and more rooted in their communities -- time-honored factors in predicting turnout.
On the other hand, analysts wonder how many of the excited young voters who registered to vote for Barack Obama -- many from the Philadelphia region -- will go to the polls in a relatively low-interest gubernatorial primary.
Mr. Yost said 18 years of data collected by Franklin and Marshall show that only in 2002 -- when Rendell was on the ballot -- did the Philadelphia region carry its weight in a primary.
Analysts attribute long-term Democratic gains to two main factors -- the anger of moderate Republicans and independents toward former President George W. Bush, and the surge of new voters who registered to help elect his Democratic successor, Mr. Obama.
Mr. Yost used his data to compare Pennsylvania voters in 2002 to the current crop. He found that Democrats are slightly younger on average, slightly less likely to identify themselves as either Catholic or Protestant, and slightly less likely to oppose abortion under all circumstances.
The party has grown "less conservative -- not necessarily more liberal, but more moderate," Mr. Yost said.
T.J. Rooney, the Democratic state chairman, said the changes could make differences "on the margins" in the primary. He didn't foresee a big impact.
"I think the Republican Party has been far more affected by its shift to the right than we have been advantaged by getting a little bit younger, a little more suburban," Mr. Rooney said.
When moderate Sen. Arlen Specter switched from a Republican to a Democrat last year, he said he felt he could no longer win in a party that had nominated him five times going back to 1980.
Mr. Specter said he hadn't changed; the party had.
The change is most evident in the Philadelphia suburbs, where the typical country-club Republican of the past was conservative on money issues but moderate on social issues.
In 2002, the five-county region had 1 million Republicans; today, it's 873,000, a loss of 13.5 percent.
Many moderates have either fled to the Democratic Party or become independents, who can't vote in either party's primary.
In southwestern Pennsylvania, GOP membership has remained stable, even edging up by about 1,000 registrants.
With the losses in the southeast, and with the Southwest at least holding its own, the Republican balance of power has tilted toward the Pittsburgh area.
The party's front-runner for governor, state Attorney General Tom Corbett, is generally viewed as a moderate.
Eight years ago, analysts say, Mr. Corbett might have felt free to basically ignore his long-shot opponent, state Rep. Sam Rohrer of Berks County.
But Mr. Rohrer has sought to capture the voter mood reflected by the antitax, anti-big-government activists of the tea party movement. That movement didn't exist in 2002.
Perhaps to guard his right flank, Mr. Corbett has taken steps that have helped buff up his conservative credentials.
He signed a pledge not to raise any taxes as governor. He joined 13 other attorneys general, mostly from Republican states, in pursuing a constitutional challenge to the new federal health-care legislation enacted by Mr. Obama and the Democrats.
Robert A. Gleason Jr., the state GOP chairman, said Mr. Corbett's moves were good public policy -- as well as good politics in a Republican primary.
"I don't think he's trying to appeal just to conservatives," Mr. Gleason said. "We still have a lot of moderates in our party. ... Main Street Republicans are just a little more conservative than they were eight years ago."