For many years, the Ontario NDP was the most successful provincial NDP branch outside the national party's western heartland. It had its first breakthrough under its first leader, Donald C. MacDonald in the 1967 provincial election, when the party elected 20 Members of Provincial Parliament (MPPs) to the Ontario Legislative Assembly. After the 1970 leadership convention, Stephen Lewis became leader, and guided the party to Official Opposition status in 1975, the first time since the Ontario CCF did it twice in the 1940s. After the party's disappointing performance in the 1977 provincial election, that included losing second party status, Lewis stepped down and Michael Cassidy was elected leader in 1978. Cassidy led the party through one campaign, the 1981 election. The party did poorly again, and Cassidy resigned.