Holt replaced Menzies as prime minister in January 1966, with McEwen continuing on his previous position. His portfolio had been expanded after the 1963 election, with his department now called the Department of Trade and Industry. McEwen enjoyed a "sound working relationship" with Holt, but without the same rapport he had had with Menzies. However, he had a poor relationship with William McMahon, Holt's replacement as Treasurer. They had philosophical differences over free trade and foreign investment, both of which McEwen opposed. McMahon was also suspected to be undermining McEwen through his connections in the media.