Three reasons for Roosevelt's break with Taft.
1) As Roosevelt' successor, he did not follow Roosevelt's agenda. Instead of demanding new legislation from Congress, Taft opted to execute the existing laws.
2) Taft alienated Roosevelt by attempting to break up U.S. Steel, a trust that Roosevelt has approved as President.
3) Taft jeopardized Roosevelt's gains in the conservation of natural resources when he forces Roosevelt's forestry chief to resign.