After knocking on doors at a half-dozen houses, Mardi Harrison, a campaign volunteer for Barack Obama, finally found someone to listen to her pitch.

Anyone who wants to vote for Obama in Pennsylvania’s primary must be registered as a Democrat, she explained to the woman who answered the doorbell. Did the independent voter at this address want to sign up?

The woman laughed and made it obvious that no one there had any use for Obama. “Yeah, you have the wrong house!” she said. And she shut the door.

Obama trails Hillary Rodham Clinton by a large margin in Pennsylvania, site of the next Democratic presidential contest. The state has a large number of the older and blue-collar voters who tend to back Clinton. Even this month’s most favorable poll for Obama shows her leading by 11 percentage points. One poll has her ahead by 26.


For Obama to win the April 22 election, or even to keep the race close, he needs to pull off an extraordinary feat: identifying sympathetic independent and Republican voters, and persuading them to register as Democrats. The registration deadline is Monday.

With time running out, the Obama campaign is engaged in a house-by-house appeal.

While Harrison and other volunteers often get a cool reception, there are some signs of progress. Statewide, the number of Pennsylvanians switching affiliation to the Democratic Party has boomed, with 57,651 signing up this year through March 14.

There is no way of knowing whether these voters are jumping to the Democratic Party to vote for Obama, but his campaign hopes that is the case. If turnout for the primary is 50%, as some analysts expect, these new converts would account for about 3% of the total vote -- and presumably a larger share of Obama’s tally.


And the trend has accelerated. More than 22,000 registered as Democrats during the week of March 10, compared with 7,223 in the entire month of January.

“I’ve never seen numbers like this in one week,” said Leslie Amoros, a spokeswoman for the Pennsylvania Department of State.

For Clinton, Pennsylvania is a must-win. With 158 delegates, the state is the largest of the 10 that have not yet voted. After nearly three months of primaries and caucuses, Clinton trails Obama by about 120 delegates.

An impressive victory in Pennsylvania would narrow that deficit while buttressing Clinton’s claim that Obama is a flawed candidate who cannot close the deal with Democratic voters. It would also help make her case that she is better positioned to win the important swing states in November.


Those arguments might resonate with the superdelegates -- the party officials and insiders whose votes ultimately are expected to decide the nomination.

If she loses Pennsylvania,” said Joe Trippi, an advisor to former Democratic candidate John Edwards, “I don’t think there are many people left who carry water for her who’ll think she has much of a shot.”

About 200 Clinton campaign aides who arrived earlier this month have been deployed throughout Pennsylvania. A handwritten sign on a wall at Clinton’s Philadelphia office reads: “Phone All Day, All the Time.”

(Neither campaign will reveal the full number of staff members in the state.)


Last week, Clinton volunteers called voters from campaign-issued cellphones, as land lines had yet to be hooked up. Amid some scattered successes, there was one volunteer stopped to tell others about the voter who said, “I am pro-life and I wish you would tell Hillary: If you kill babies you don’t have a country.”

One of the New York senator’s most potent assets is her husband. As president in the 1990s, Bill Clinton spent considerable time in Philadelphia and made durable allies. The mayor at the time, Edward G. Rendell, had a strong rapport with him. And Rendell is now well positioned to help the campaign as a second-term governor.

But as he visits the city, the former president is finding a changed political landscape. Black leaders once loyal to the Clinton family are defecting to Obama. Census figures show Philadelphia to be 46% African American. When Bill Clinton spoke to the city’s Democratic ward leaders March 7, the reception was chillier than he was used to.

State Sen. Anthony H. Williams told the former president in the closed-door session that he was concerned about racially tinged comments Clinton made in South Carolina. During that contest, the former president likened Obama to a failed black presidential candidate from another era, Jesse Jackson. Williams told Clinton that he did not want politicians to send children a message that “caps their dreams.”


The former president became visibly annoyed and said that the media had misconstrued what he had said, according to Williams and others who were there.

The Obama campaign is following a blueprint that looks similar to one employed by Rendell in his 2002 faceoff with Bob Casey in the Democratic primary for governor. Rendell won by running up huge margins in Philadelphia and suburban counties in the same media market.

Some Pennsylvania political experts are skeptical that the same plan will work for Obama. A more realistic goal, they said, would be a loss of 5 or 6 percentage points, keeping Clinton from running off with a large cache of delegates.

“I don’t think that Obama can roll up the same types of numbers that Ed did in the city and especially the suburbs,” said Larry Ceisler, a Democratic political consultant. “Ed had been a fixture in this media market for 16 years. Obama is not going to come up with those types of numbers in the Philadelphia suburbs.”


The Illinois senator hopes to beat such expectations by expanding the pool of Democratic voters.

One night recently, some Obama volunteers in Doylestown set about making calls to find people willing to sign Democratic registration forms. A script provided by the campaign said that if voters were undecided, the callers should note that “Sen. Clinton has said there’s a choice in this race. And she’s right. It’s a choice between a politics that offers more of the same divisions, or a new politics of common purpose.”

The work is often futile. Volunteer Naomi Plakins, 59, a medical malpractice lawyer, said one woman on the phone barked: “This is GOP country.” Slam.

But every once in a while there was a small success. After finishing one call, Plakins threw up her arms and squealed: “Yes! He wants the form!”


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peter.nicholas@latimes.com