With redistricting in 2012, the 164th District changed to include Lansdowne and parts of Yeadon in addition to parts of Upper Darby Township, East Lansdowne, and Millbourne.
The winner of the Democratic primary will oppose Republican Saud Siddiqui, CEO of the Upper Darby Caring Foundation. But "the real election might be the primary," said Randall Miller, a history professor at St. Joseph's University, because the district is firmly Democratic.
Smith said he decided to run after researching Davidson's record. He has cast himself as the pro-choice and anti-school-voucher candidate.
"I bring these points up . . . to say, 'Is this who you want, Mr. and Mrs. Democrat in the 164th District, representing your interests?'" Smith said in an interview.
With the addition of Lansdowne, the district is "in the process of forming an identity, and Smith played on that," Miller said.
Smith, who has the backing of Planned Parenthood, sent mailers comparing Davidson's views on abortion to those of Rush Limbaugh and Sarah Palin. He said laws adding restrictions on women's health clinics are attempts to limit access to abortion.
Davidson, 51, of Upper Darby, stands by her votes and considers herself pro-choice. She received national media attention 2011 when she spoke on the House floor about her cousin, one of the women killed in Kermit Gosnell's West Philadelphia clinic. She said she voted to make abortions safer.
"I don't want another family or another woman to have to go through that in the state of Pennsylvania - not if I can help it," Davidson said.
Zhang said he was pro-choice and would not have supported additional restrictions on abortion clinics.
Davidson's opponents also disagree with her on the school-choice issue.
She was one of just four Democrats who cast a vote in favor of school vouchers in 2011; the legislation did not pass. She said she supported school choice because families in poorly performing school districts should have other options.
"I support schools that are doing well, whether they be public, private, charter, parochial," said Davidson, who has received campaign donations from Students First, a political action committee in Pennsylvania that advocates for school vouchers.
Smith said he opposes school vouchers. He said fighting for education funding means fighting to put more money directly into public schools.
"Our schools are woefully underfunded," he said. "We need to have a progressive coalition of Democrats in Harrisburg who are going to fight tooth and nail to ensure that children have, regardless of their financial circumstance, the best access to quality education."
Zhang said he supported funding only for public education, and opposes both vouchers and charter schools.
Smith has accused Davidson of helping Gov. Corbett cut funding to public schools - a claim she challenges.
Davidson was one of a handful of Democrats to vote in favor of the state budget in 2012; she said she cast that vote because it included funding that she had sought for the Upper Darby and William Penn School Districts. She voted against the 2011 state budget that included cuts to education funding.
Smith and Davidson each have a number of endorsements. Smith's include the Pennsylvania State Education Association, the state's largest teachers' union, and Philadelphia District Attorney Seth Williams, who supervised Smith when he worked in the District Attorney's Office. Davidson has earned backing from the Delaware County Democratic Committee and several labor unions.
Zhang, a newcomer to politics, said he was focusing on his own experiences rather than his opponents. He came to the United States from China to attend high school, but dropped out and was homeless in Philadelphia. He is preparing to graduate from law school this month.
"I want to make a difference," Zhang said. "If I get elected in office, you will definitely know who I am."
By the Friday campaign finance report deadline, Zhang reported only $660 in donations and $1,198 in cash on hand. By contrast, Davidson reported $64,285 in donations and had $31,592 on hand. Smith had raised $48,515 with $15,571 on hand by the deadline, but has since reported an additional $27,140 in donations, including $20,000 from PSEA.
The 164th District is the only contested primary race in Delaware County. In the November election, Delaware County Council Chairman Tom McGarrigle and John Kane, business manager of Plumbers Union Local 690, are running for an open seat to replace retiring State Sen. Edwin "Ted" Erickson. Republican State Rep. Nicholas Micozzie of Upper Darby is also retiring; Republican Jamie Santora and Democrat Vince Rongione are running for the open seat.