ST. PAUL, Minn. (AP) — U.S. Rep. John Kline said Thursday he wouldn't seek re-election next year, sparking immediate speculation of potential candidates for the southeastern Minnesota seat he occupies.

More than a dozen GOP legislators from the area, and several instantly sprang into consideration mode. A Republican from the party's libertarian flank, David Gerson, was building toward a primary challenge for the second consecutive election cycle.

Two Democratic candidates had lined up to challenge Kline, stockpiling cash for what was expected to be an expensive race. Angie Craig, an executive at a medical device manufacturer who is openly gay, registered her campaign in January. Minneapolis doctor Mary Lawrence followed suit in the spring. The national House Democratic campaign arm had Kline's district on its 2016 radar as a pickup opportunity.

Kline's departure opens the door for more challengers — from both parties — to enter the race.

Democratic state Rep. Joe Atkins has been recruited for years to challenge the incumbent Republican. Atkins said Kline's retirement wouldn't influence his decision and said he planned to make an announcement about his plans next week.