Lots of people want to run for Congress in Pennsylvania this year, but they may not yet know which district they live in.

The prospect that the state Supreme Court could decide a high-profile gerrymandering case by ordering new boundaries for Pennsylvania's 18 congressional districts is sowing uncertainty barely a month before candidates begin circulating petitions.

Primary fields could be jam-packed, driven by Democrats' anti-Trump fervor and a rush to fill the most open seats in Pennsylvania in decades.

On Wednesday, Pennsylvania's Supreme Court will hear arguments in the seven-month-old case urging the court to throw out Pennsylvania's congressional districts as an unconstitutional gerrymander that unfairly favors Republicans.

The court has a 5-2 Democratic majority.