Hillary and Marco, Bernie and Donald, and the 2016 presidential race already may be on voters' minds, but first Pennsylvanians have decisions to make in the 2015 elections.

If patterns hold, only about 25 percent of them will cast ballots Tuesday. Along with county judges, prosecutors, commissioners, and other officials, they will choose an unprecedented number of Supreme Court justices.

Among the higher-profile races are those for district attorney in Montgomery County - where Bill Cosby has become an issue - and for mayor of Chester City.

Statewide, attention will be focused on the Supreme Court, where three seats are simultaneously up for grabs for the first time in three centuries.

More than $10 million has been spent on the campaigns for the high court, where justices could soon be asked to decide cases on the death penalty, legislative redistricting, and natural gas drilling.

"These are positions that will have a significant influence over the next several decades on issues that people care about," said David Thornburgh, president of the Committee of Seventy, the nonpartisan watchdog group. Thus, he said, Tuesday's election is "a unique opportunity."

The candidates are Superior Court Judges Christine Donohue, David Wecht, and Judy Olson; Commonwealth Court Judge Anne Covey; Philadelphia Common Pleas Court Judges Kevin Dougherty and Paul Panepinto, and Adams County Court Judge Mike George.

Donohue, Wecht, and Dougherty are Democrats; Olson, Covey, and George are Republicans.

They aren't running in slates but have campaigned together. After failing to win the GOP endorsement, Panepinto decided to run under the Independent Judicial Alliance party.

In a presidential battleground state, Tuesday's municipal outcomes will be of national interest - especially given recently shifting political tides. Traditionally, the GOP has counted on Philadelphia's neighboring counties to neutralize Democratic majorities in the city. But after decades of GOP dominance, registered Democrats now outnumber Republicans in Bucks, Delaware, and Montgomery Counties.

Chester County is the only one with a GOP plurality, and that margin has been shrinking.

"There isn't any doubt the Democrats have been on the move," said G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin and Marshall College.

In past years, Bucks, Delaware, and Montgomery Counties helped send Barack Obama to Washington and Tom Wolf to Harrisburg. But the flip to blue has been less evident in local elections, and Madonna said he doesn't see that changing significantly Tuesday.

Turnout is key. In the 2011 elections, only about 25 percent of the state's eligible voters cast ballots, and the GOP generally has the edge in off-year election turnout.

"Our concentration is more on the get-out-the-vote than it is on the message," said John Cordisco, chair of the Bucks County Democrats.

Along with lower turnout, Democrats remain at stark financial disadvantages. Combined, the Republican committees in the counties have managed to raise more than twice as much as their Democratic counterparts this year.

In Delaware County, where Wolf took 61 percent of the vote in 2014, Democrats are fighting to regain relevance in county government and capitalize on what they say is a lack of accountability after decades of one-party rule.

Yet they have raised about a quarter as much as the GOP committee this year.

Three GOP incumbents for County Council - John P. McBlain, Colleen P. Morrone, and Mike Culp - are opposed by Democratic challengers Christine Reuther, Sharon Booker, and Richard Womack. Democrats haven't had a seat on the council since Jimmy Carter was president.

In Chester, the county's only city, 12-term state legislator Thaddeus Kirkland - who defeated the Democratic incumbent in the primary - is running against Republican former Mayor Wendell Butler.

Another veteran legislator and erstwhile Harrisburg power-broker, Republican former Senate Majority Leader Dominic Pileggi, is seeking a county judgeship.

In Bucks, Democrats gained the registration edge in 2008, but Republicans still hold every row office and the majority on the board of commissioners.

County Commissioners Charles H. Martin and Robert G. Loughery, both Republicans, and Diane Ellis-Marseglia, a Democrat, are running to keep their seats; Democrat Brian Galloway, an elementary school principal, is also in the race.

Gains for Democrats have been most robust in Montgomery County - the only one of the four where Democrats have more money than their rivals.

They are hoping to take the District Attorney's Office, which could prosecute not just one but two high-profile cases: those against Attorney General Kathleen G. Kane and comedian Bill Cosby. Democrat Kevin Steele, who is current D.A. Risa Vetri Ferman's first assistant, is running against Republican Bruce L. Castor, a county commissioner and Ferman's predecessor. Ferman is running for a county judgeship.

The two Democratic incumbents for county commissioner, Josh Shapiro and Valerie A. Arkoosh, are running for reelection on a joint ticket. Republicans Steve Tolbert and Joseph Gale are running separately.

The GOP still dominates in Chester County, the only one of the five counties with more Republican voters registered than Democrats. Republicans have raised the most of any county party organization - nearly $700,000 - more than the combined total raised by Chester County Democrats since 2008.

The GOP holds all the row offices, and incumbents are up for reelection in nearly every race.

In the most competitive race, Democrat Julia Malloy-Good and Republican Allison Bell Royer will vie for a single open county court seat. In 2013, Malloy-Good lost by a mere 2 percentage points.

Otherwise, Democrats are challenging a strong slate of incumbents. District Attorney Thomas Hogan, who took over from a Republican predecessor in 2012, will face Democrat Tom Purl, a private attorney.

The regional blue tide is giving Chesco Democrats reason for optimism. Their chairman, Brian McGinnis, believes Democratic registered voters could outnumber Republicans within the next year.

"We're very close," he said. "The majority of the county right now isn't Republican, it's Democrat and Independent.

"That's the first time in history that that's happened."