Borden appointed Alberta Liberal William Harmer to the Senate to satisfy the Unionist coalition agreements. Bennett was reportedly furious at this move, believing that Borden broke a promise to appoint him to the Senate. Bennett wrote Borden a resentful 20-page letter. Borden never replied. Borden's successor, Arthur Meighen, appointed Bennett minister of justice on September 21, 1921. In the federal election two and a half months later, Bennett ran for the riding of Calgary West, but lost by 16 votes. In this election, the Conservatives sunk to third place. Bennett developed an extensive legal practice in Calgary. In 1922, he started the partnership Bennett, Hannah & Sanford, which would eventually become Bennett Jones LLP. In 1929–30, he served as national President of the Canadian Bar Association. By the mid-1920s, Bennett was on the board of the Royal Bank of Canada (RBC). He was also a director of Metropolitan Life Insurance of New York. Political return and leader of the Official Opposition (1925–1930) After Meighen, who was attempting to become prime minister again, offered Bennett to be minister of justice, Bennett ran for and won the seat of Calgary West in the 1925 federal election. The Conservatives won the most seats but didn't have a majority. They didn't necessarily form government due to Liberal Prime Minister William Lyon Mackenzie King negotiating support from the Progressive Party. However, in the summer of 1926, the Conservatives were invited to form government by Lord Byng. Byng refused King's request to dissolve parliament and call an election, and thus King resigned. On July 2, the Meighen government was defeated in a motion of non-confidence by one vote, triggering an election scheduled for September 14. At the time of the confidence vote, Bennett was in Alberta campaigning on behalf the province's Conservative Party for the provincial election, and thus was unable to vote against the motion. Meighen greatly regretted his absence and later wrote, "If Mr. Bennett had been there... King would never have talked the diabolical and dishonest rot in which he indulged. He was a lot more careful when Bennett was across the floor...". In the election, the Liberals decisively won. In Meighen's short-lived government, Bennett served as minister of finance along with numerous acting portfolios. After this defeat, Meighen stepped down as Tory leader, triggering a leadership convention scheduled for October 1927. Bennett ran for and won the leadership on the second ballot