In the Eismann family alone, the Democratic Party can count three new registered voters.

Or maybe it's four.

Virginia Eismann, a homemaker whose husband runs a wood-flooring business, said she wasn't sure whether their younger son, a 21-year-old college student, submitted his voter form in time.

If he did, "then there's one more of us," she said.

The Eismanns, of the Doylestown area, are among the tidal wave of people in the five-county Philadelphia region - former Republicans, former independents, former nonvoters - who registered as Democrats to vote in Tuesday's primary. And the majority of these newly registered voters appear to support Sen. Barack Obama, according to a recent poll.

The headlines are well-known: For the first time in decades, Democrats outnumber Republicans in Montgomery and Bucks Counties. And Democrats and independents, grouped together, now outnumber Republicans in the two remaining suburban counties: Chester and Delaware.

But the significance of the Democratic gains goes far deeper.

A close analysis of state voter-registration data from April 6 compared with April 2007 shows just how sweeping the changes are.

Democrats increased their party enrollment in 99 percent of the zip codes in the region, while the number of Republicans declined in 92 percent of zip codes.

Independents, many of whom have been voting as Democrats for years in fall elections, switched in large numbers to get a piece of the primary action in the race between Obama and Sen. Hillary Rodham Clinton. The number of independents dropped in 90 percent of zip codes.

At the same time, the Democrats continued a decade-long trend of gaining the upper hand, registration-wise, in more and more townships and boroughs.

Among the 238 municipalities in the five-county area, Republicans still hold a plurality in 181. But compared with this time last year, the Democrats have become top dogs in 15 additional municipalities - for a total of 57.

The biggest of the communities that have flipped party plurality since this time last year is Upper Dublin Township in Montgomery County. There, percentage-wise, the Republicans held a 45-41 advantage last April. Now, they are at a 41-46 disadvantage.

Other communities that have flipped include two townships similar to Upper Dublin - Plymouth and Whitemarsh, both classic, postwar suburbs near the border with Philadelphia.

Also on the list are a wide range of older boroughs - crossroads towns that run from economically modest Eddystone and Hulmeville to well-off Doylestown.

John J. Kennedy, associate professor of political science at West Chester University, noted that each of the 15 communities with a new Democratic registration edge voted for Democrat John Kerry over President Bush in 2004.

"People change their voting patterns first," he said. "It may take years - decades - before they change their registration, and then usually there is some watershed event to make it happen."

The Obama-Clinton race appears to be just such an event - not only in the region, but statewide.

Pennsylvania now has 8.3 million voters, of whom 4.2 million are Democrats and 3.2 million are Republicans. The Democrats have gained 326,756 voters since a year ago, and the Republicans have lost 73,009.

In the five-county Philadelphia region, the Democrats gained 140,000 voters and the Republicans lost 42,000 over the last year.

Virginia Eismann, a former independent, said that a Democratic worker - a woman who appeared to be in her late 60s - came to her door in the Fieldstone Place section of Buckingham Township, outside Doylestown.

"She said she had been to 60 homes in our area, and 90 percent of them had switched," Eismann recalled.

The woman had blank voter-registration forms with her. Eismann signed, on the spot, to become a Democrat.

She has been an irregular voter, she said. But "the past seven years" of the Bush administration have made her angry, she said.

She plans to vote for Clinton. Her husbands and sons, she said, will likely vote for Obama.

Both Clinton and Obama worked hard before the primary registration deadline on March 24 to sign up voters apt to favor them.

A recent Keystone Poll of Pennsylvania voters, conducted by Franklin and Marshall College, found that 62 percent of Democrats who registered statewide within the last three months planned to vote for Obama.

Kennedy said it made sense that the surge in new registrations would be more a result of Obama's candidacy than Clinton's.

"Clinton is a known quantity; she had been in the public eye for 15 years," he said. "Obama is the new face."

The question is: How many of the new Democrats will switch back to Republicans - or independents - when the primary is over?

Republican Bruce L. Castor Jr., the top vote-getter in Montgomery County last year as a candidate for county commissioner, said he wasn't sure what would become of former independents.

But he predicted that a great many former Republicans would "come back" to the GOP fold.

"The Republicans that are changing, as near as I can tell, are changing so they can vote against one of the Democrats," he said. "I am hearing people saying they are switching to vote for Obama or for Clinton on the theory that one or the other of them is more vulnerable to [Sen. John] McCain in the fall."

Larry Ceisler, who has been an adviser to Democrats, said he doubted that many of the party-switchers would go back.

"There is no doubt in my mind that people are changing to vote for president," he said. "But once they change their party, it's very difficult to bring them back."

New Democratic Pluralities

These 15 municipalities shifted from a Republican to a Democratic plurality in the

last year:

Caln

Darby Borough

Downingtown

Doylestown Borough

Hulmeville

Kennett Square

Lansdale

Media

North Wales

Parkesburg

Plymouth Township

Riegelsville

Upper Dublin

West Conshohocken

Whitemarsh

SOURCE: Pa. Department of State; Inquirer analysisEndText

Contact staff writer Dylan Purcell at 215-854-4915 or dpurcell@phillynews.com.