HARRISBURG, Pa. (AP) -- Pennsylvania's congressional races are in full swing, while Republicans are waging legal battles in federal courts in an effort to block a new map of 18 districts imposed by the state Supreme Court.
That has added a layer of uncertainly to fields of candidates that already went through upheaval when the state's high court redrew boundaries last month, putting the homes of some congressional hopefuls into different districts or forcing them to rethink their candidacy.
Primary fields are crowded, and dozens of people are collecting signatures to get on primary election ballots.
Some candidates are running in districts where they don't live in order to improve their chances of winning. Some dropped out, while others decided to run in their new district or seek another office. The fields are dynamic: on Friday alone, several candidates dropped out or announced that they would run in a different district.
The election has national implications, as Pennsylvania Democrats believe the court's map gives them an improved playing field to win seats in Congress and boost the party's chances at erasing the GOP's U.S. House majority in the fall election.
WHAT ARE THE BIG DATES?
The deadline for candidates to file 1,000 signatures of qualified registered voters is March 20. The primary election is May 15.
WHAT'S GOING ON WITH THE LAWSUITS?
At the U.S. Supreme Court, Justice Samuel Alito has given the new map's defenders -- the Democratic voters who successfully challenged Pennsylvania's congressional map in state courts -- until Monday to respond to a Republican effort to block its use.
Republicans argue that the court overstepped its authority in throwing out the six-year-old Republican-drawn map, and gave lawmakers too little time to craft their own replacement.
Republicans are also asking a panel of lower federal judges to immediately throw out the map. The next hearing in that case is Friday.
The state Supreme Court's ruling was indeed novel: Constitutional law scholars say they know of no other state court that has ever thrown out congressional district boundaries over a partisan gerrymandering claim without an express state constitutional provision prohibiting partisan favoritism in redistricting.
WHAT HAPPENED WITH THE OLD MAP?
The Democratic majority on Pennsylvania's high court ruled that its boundaries violated the elections clause of the state Constitution, which guarantees that elections "shall be free and equal." Justice Debra Todd wrote that a map of congressional districts violates that clause when neutral line-drawing standards, such as compact and contiguous districts, are subordinated for unfair partisan political advantage.
Republicans who controlled the Legislature and governor's office in 2011 redrew the districts in an effort to get Republicans elected. They drew bizarrely contorted boundaries that are very effective: Republicans won 13 of 18 congressional seats in three straight elections in a stretch when Democrats won 18 out of 24 statewide elections in Pennsylvania.
WHERE ARE THE HOT RACES?
Twelve incumbent congressman and dozens of other people have filed to run. Some primary fields are jam-packed, driven by a rush to fill six open seats, the most in Pennsylvania in four decades, as well as by seats that are more competitive under the court's new map.
Two Republican incumbents are facing difficult re-election contests in increasingly liberal districts: Rep. Brian Fitzpatrick in the Bucks County-based 1st District and Rep. Ryan Costello in the Chester County-based 6th District.
Democratic primary fields are particularly crowded in the Montgomery County-based 4th District, the Delaware County-based 5th District, the Allentown-based 7th District, the Harrisburg-based 10th District and the suburban Pittsburgh-based 17th District.
Two of those five districts are home to a Republican incumbent: Rep. Scott Perry in the 10th and Rep. Keith Rothfus in the 17th. But both districts were made more competitive under the court's new map. A Democratic victory in the 5th or 7th District will mean that Democrats captured a formerly Republican seat.
Meanwhile, Republican primary fields are crowded in two districts -- southwestern Pennsylvania's 13th District and eastern Pennsylvania's 9th District -- where Republican candidates are heavily favored and the Republican incumbent is not running for re-election.