HARRISBURG - Unseating first-term Republican U.S. Sen. Pat Toomey won't be easy, and the Pennsylvania Democrats vying for the party nomination will first have to figure out how to capture voters' imagination.

None of the three - Joe Sestak, Katie McGinty and John Fetterman - are household names or have held statewide office. They are also virtually identical on bedrock Democratic Party issues, from supporting the Affordable Care Act and abortion rights to backing President Barack Obama on immigration reform and climate change.With less than five months until the April 26 primary, the unpredictable mood of the electorate may determine how Democrats will choose among the candidates, analysts and party strategists said."I don't think you can rule that out as a motivating factor if the candidates don't have enough to differentiate themselves," said Terry Madonna, a pollster and political science professor at Franklin & Marshall College in Lancaster.Registered Democrats outnumber Republicans in Pennsylvania by a 4-3 ratio, and beating Toomey will be of the utmost importance for Democrats to retake control of the Senate. The race is expected to be nationally watched, with tens of millions of dollars pouring in, mostly for TV ads.For now, Toomey appears to be uncontested in the primary and backed by a unified Republican Party.Each of his potential Democratic foes has strengths.In a sense, Sestak, 64, never stopped running for a rematch with Toomey. He retired from the Navy in 2006 after reaching the rank of vice admiral and went on to serve two U.S. House terms from Delaware County. In 2010, Toomey beat him by 2 percentage points, but he built a volunteer network and he has maintained good will among rank-and-file Democrats after becoming a regular on the local party event circuit.The ability to raise money will be of prime importance, and McGinty, 52, could be the Democrats' best fundraiser. Senior party officials and donors recruited her and she has strong connections to top Democrats - she served as a top aide to former Gov. Ed Rendell, current Gov. Tom Wolf and in the Clinton White House. She ran for governor in 2014, finishing fourth in the four-way primary.Fetterman is a newcomer to statewide electoral politics and virtually unknown in eastern Pennsylvania, but he is a national media darling for his unconventional efforts to revive the impoverished, dying Pittsburgh-area steel town of Braddock where he has been mayor since 2005. The 46-year-old is also bound to be popular with younger voters: He's 6 foot 8, tattooed with a shaved head and goatee, and is most often seen in a black Dickies work shirt, cargo shorts and work boots.The shrinking middle class is a key campaign focus of all three candidates, and Fetterman isn't pulling punches in his efforts to highlight his career in Braddock."They say they're for the middle class, but I'm not sure what in their professional background supports that," Fetterman said.For McGinty, her parents' blue-collar roots are a prominent theme."I'm in this race to stand with working families and to rebuild the middle class," McGinty said. "It's personal for me. As the ninth of 10 kids and the first in my family to go to college, I've been privileged to live the American dream."Sestak's campaign makes much of the theme that he is "walking in your shoes" after he kicked off his campaign last spring by walking across the state."I wanted to show people that I would walk in their shoes and understand their hopes and concerns, their challenges," Sestak told a WILK-FM radio interviewer last month.The middle class aside, Sestak could benefit if the fight against terrorism shapes the election. His national security credentials are a campaign emphasis - staff aides refer to him "the admiral."Should breaking the glass ceiling become a driving theme - and it could if Hillary Clinton seals the presidential nomination - that could favor McGinty. Pennsylvania has never had a female U.S. senator and men make up Pennsylvania's entire 19-member congressional delegation.If the voters seek out a Bernie Sanders-style anti-politician, then Fetterman could be their man.In the meantime, two important dates could help determine the relative strengths of the candidates: the Jan. 15 deadline to disclose their latest campaign fundraising performance, and Jan. 23, when state party committee members could consider a primary endorsement vote.Feb. 16 is the deadline to file enough signatures to get on the ballot.