Washington was elected to the Senate in 2005, and to the House in 1993, through special elections.
Gralnick and Haywood are pushing for greater funding for Philadelphia schools, improvements in senior services, and a raise in the minimum wage.
Washington and her campaign organizers could not be reached for comment.
Gralnick said he had considered public office for a long time, but decided to jump into the Senate race after The Inquirer reported that Washington was under investigation and had been absent for about one-third of the 2012-13 legislative session.
Washington was charged March 12 with using Senate staff and resources to work on her campaign fund-raisers from 2005 to 2013. A grand jury report estimated the cost to taxpayers was $30,000 to $100,000.
The senator has vowed to fight the charges.
The Fourth Senate District spans Northwest Philadelphia, including Germantown and Mount Airy, and southeast Montgomery County, including Abington, Cheltenham, and, through this year's redistricting, Springfield Townships.
All four of the candidates live in Cheltenham, including Washington, who moved in November from a single-family house in the Cedarbrook section of Philadelphia to a penthouse apartment in Wyncote.
Political experts say the charges make Washington's road to reelection look bumpy, but not impassable.
"We've seen elected officials under indictment win elections because they're very popular with their constituents," said Chris Borick, a political science professor at Muhlenberg College.
"Just because someone is facing criminal charges does not mean they are not going to win an election," said Ellen Kaplan, director of the election-watchdog group Committee of Seventy. "It's very difficult to topple incumbents."
Washington still has the backing of many colleagues and Democratic leaders in Harrisburg and Philadelphia. She earned praise as the only legislator to turn down the infamous 2005 pay raise, and for advocating against child abuse and domestic violence, as a survivor of both.
Borick said a personal connection to voters was key to overcoming a scandal such as Washington's.
"As a follower of state politics," Borick said, "she isn't a household name and a presence in the Senate by most measures."
Said Gralnick: "She's not visible in the district, nor is her staff. I've been very active in this community over 10 years, and rarely have I seen her."