That has haunted him as the party flatlined in polls, while Merkel's conservative Christian Democrats are strong and the chancellor is fortified by her handling of the debt crisis and a strong economy. Merkel's center-right coalition lacks a majority in national polls, but they suggest she may well be able to keep power after September by seeking a new partner.
Speculation has swirled for months that Roesler, 39, would have to go if the FDP does badly in Lower Saxony, and carping from members has intensified recently. Development Minister Dirk Niebel vented his frustration about the situation in a speech to Sunday's event, insisting that the party can't wait until a scheduled convention in May to choose its election campaign team.
"Things can't carry on in the FDP as they are now," he said. "It tears me up inside when I see the state of my, our FDP."
Roesler said that credibility is "also a question of style, fairness and solidarity." He urged the party to "send a signal that we are ready to fight together" in Germany's election year.