Harold Holt disappeared while swimming on 17 December 1967 and was declared presumed drowned two days later. His presumed successor was Liberal deputy leader William McMahon. However, on 18 December, the Country Party leader and Deputy Prime Minister John McEwen announced that if McMahon were named the new Liberal leader, he and his party would not serve under him. His reasons were never stated publicly, but in a private meeting with McMahon, he said "I will not serve under you because I do not trust you". McEwen's shock declaration triggered a leadership crisis within the Liberal Party; even more significantly, it raised the threat of a possible breaking of the Coalition, which would spell electoral disaster for the Liberals. Up to that time, the Liberals had never won enough seats in any House of Representatives election to be able to govern without Country Party support. Indeed, since the Coalition's formation in 1923, the major non-Labor party had only been able to govern alone once, during Joseph Lyons' first ministry. Even then, Lyons' United Australia Party had come up four seats short of a majority in its own right, and was only able to garner a bare majority of two when the five members of the Emergency Committee of South Australia joined the UAP party room.