Clark ran for House Minority Leader in 1903 but was defeated by John Sharp Williams of Mississippi. After Williams ran for the Senate in 1908, Clark ran again for the position and won. When the Democrats won control of the House in 1911, Clark became Speaker. In 1911, Clark gave a speech that helped to decide the election in Canada. On the floor of the House, Clark argued for the recent Canadian–American Reciprocity Treaty and declared: "I look forward to the time when the American flag will fly over every square foot of British North America up to the North Pole."