On April 15, Lévesque announced before the National Assembly the referendum would occur on May 20, 1980. The same day, on the opening of the House of Commons, Trudeau announced that the Government of Canada would not negotiate sovereignty-association under any circumstances, as he considered the question too vague and the Canadian government's authority too uncertain to do so. He also stated that the question was too vague to give Lévesque and the PQ any mandate to declare independence, making any result from a "Yes" vote impossible; in contrast, he offered that a "No" vote would lead to constitutional change. His position was supported by Clark and national NDP leader Ed Broadbent.