OTTAWA — Liberal MPs spent Wednesday behind closed doors pressing the party to change its rules so that only citizens and permanent residents can vote for its next leader, which they argue is necessary to guard against the threat of foreign interference.

Eligibility was but one of the factors caucus discussed about the terms of the imminent race to replace Prime Minister Justin Trudeau, who faced his caucus for the first time that day since announcing on Monday he would be resigning as party leader and prime minister once his successor is chosen.