In 1958, following Fadden's retirement, McEwen was elected unopposed as leader of the Country Party. This made him the "de facto" deputy prime minister, and gave him a free choice of portfolio. Fadden had been Treasurer, but McEwen somewhat unexpectedly chose to continue on as trade minister. This allowed Harold Holt to become the first Liberal MP to serve as Treasurer; since then every Treasurer in a Coalition Government has been a Liberal. McEwen nonetheless had considerable influence in cabinet. He and his party favoured interventionist economic policies and were opposed to foreign ownership of industrial assets, which placed him frequently at odds with his Liberal colleagues. In 1962, a dispute between McEwen and Assistant Treasurer Les Bury ended with Bury being sacked from cabinet. His stature eventually grew to the point where he was considered a potential successor to Menzies as prime minister. An opinion poll in December 1963 showed that 19 percent of Coalition voters favoured McEwen as Menzies' successor, only two points behind the poll leader Holt. By December 1965, this number had risen to 27 percent, compared with Holt's 22 percent. McEwen's cause was championed by a number of media outlets, including "The Sun" and "The Australian". Nonetheless, he had few supporters within the Liberal Party, and it was generally held that he would have to become a Liberal if he were to lead the Coalition, which he was unwilling to do.