When Prime Minister Robert Muldoon called an election for July 1984 Lange led his party to a landslide victory, becoming, at the age of 41, New Zealand's youngest prime minister of the 20th century. Lange took various measures to deal with the economic problems he had inherited from the previous government. Some of the measures he took were controversial; the free-market ethos of the Fourth Labour Government did not always conform to traditional expectations of a social-democratic party. He also fulfilled a campaign promise to deny New Zealand's port facilities to nuclear-armed and nuclear-powered vessels, making New Zealand a nuclear-free zone. Lange and his party were re-elected in August 1987; he resigned two years later and was succeeded by his deputy, Geoffrey Palmer. He retired from Parliament in 1996. Prime Minister Helen Clark described New Zealand's nuclear-free legislation as his legacy.