An early poll last year showed Marjorie Margolies, who held the seat in the mid-1990s, would easily reclaim it. But her opponents - State Sen. Daylin Leach, physician Valerie Arkoosh, and State Rep. Brendan Boyle - launched vigorous campaigns, landing endorsements, running ads, and raising cash.
Margolies, whose son is married to Chelsea Clinton, has turned to the former first family for support. Hillary and former President Bill Clinton appeared at fund-raisers for her. But Margolies' campaign coffers also became an issue when Leach twice accused her of illegally dipping into general election funds to support a sagging primary campaign.
The eventual nominee is expected to square off in the fall against the winner of the GOP race between retired U.S. Air Force Col. Beverly Plosa-Bowser and businessman Carson "Dee" Adcock.
In Bucks County, two Democrats are duking it out for the chance to oust U.S. Rep. Mike Fitzpatrick, the Eighth District incumbent. Kevin Strouse, a former Army Ranger and CIA analyst, and Shaughnessy Naughton, a cancer researcher turned businesswoman, are trying to reclaim a House seat Democrats once held and have long since targeted.
In the Pennsylvania General Assembly, all 203 House members and half of the 50 senators will be up for reelection, and nearly four dozen face competition Tuesday.
Among them are three sitting Philadelphia lawmakers, all Democrats, who entered the campaign season under legal clouds.
Sen. Leanna Washington, whose Fourth Senate District is split nearly evenly between Philadelphia and Montgomery County, is under indictment for allegedly using her legislative staff to work on a campaign fund-raiser. She faces two opponents in what may be the first competitive race of her 21-year legislative career.
Washington's challengers, Cheltenham Township commissioner Art Haywood and community organizer Brian Gralnick, have attacked Washington for being ineffective and unresponsive to constituents.
Washington has maintained a low profile since being charged and has not responded to reporters' requests for interviews.
Rep. Vanessa Brown, who represents the 190th House District in Philadelphia, was among four Philadelphia lawmakers captured on tape allegedly accepting money or gifts as part of a-long running sting investigation by the state Attorney General's Office. She has two primary challengers, Wanda Logan and Isaac N. Patterson V.
Rep. J.P Miranda, who represents the 197th House District in the city, is awaiting trial for allegedly funneling taxpayer money through a ghost employee to his sister. He faces three challengers, including former City Councilman Ben Ramos.
In Delaware County, two Democrats are looking to unseat Rep. Margo Davidson, who made history in 2010 when she took office as the first African American woman in the county elected to the legislature.
Davidson, who represents the 164th District, is seen as vulnerable because she voted with Republicans on bills to restrict abortion clinics and expand school vouchers.
Billy Smith, a defense lawyer and former Lansdowne Borough councilman, is campaigning against Davidson's voting record, saying he is pro-abortion rights and against school vouchers. The second challenger, University of Pennsylvania law student Dafan Zhang, has avoided the battle over Davidson's record.
Davidson says she stands by her votes and considers herself pro-choice. The winner is expected to face Republican Saud Siddiqui, CEO of the Upper Darby Caring Foundation.
Other notable primary races in the state's southeast corner include a contest to fill a seat in the newly mapped 74th District in the Downington area of Chester County. The seat was the result of population shifts in the 2010 census.
One of the Democrats, either Joshua Young of Coatesville or Josh Maxwell of Downingtown, will face Republican Harry Lewis from Downingtown in November.
In upper Bucks County, three Democrats and one Republican seek to fill the seat left vacant by retiring State Rep. Paul Clymer, a Republican.
The winner of the Democratic field - Karen D. Chellow of Perkasie, Jon McCartney, and Brian Kline, both from Quakertown - is expected to take on Republican Harry Lewis of Quakertown in the fall.
In Philadelphia, Sen. Tina Tartaglione, a Democrat who represents the Second District, has two primary challengers - Danny Savage and Tomas Sanchez.
Democrats are backing State Rep. Ed Nielson - whose Northeast Philadelphia district seat was eliminated in legislative redistricting - in the special election to fill a seat on City Council. The at-large seat was vacated by Bill Green when Corbett named him chairman of the School Reform Commission. Nielson's Republican opponent is ward leader Matthew Wolfe.
Also on Tuesday, Philadelphia voters will be asked to vote on three ballot questions to amend the city charter.
One would allow Council to pass legislation setting minimum-wage and benefits standards for subcontractors on city contracts.
The second would end the rule that Philadelphia elected officials must resign from office to run for another position.
Question three asks whether Council approval should be required for certain contracts related to hiring legal representation for indigent defendants and clients.