Final answer:
William Taft was the president in office when portions of the National Park System were sold to lumberjacks, causing controversy and damaging his conservationist reputation.
Step-by-step explanation:
The president who was in office when portions of the National Park System were sold to lumberjacks was William Taft.
Taft's Secretary of the Interior, Richard Ballinger, approved the sale of millions of acres of federal land to a company for which he had previously worked. This decision caused controversy as it violated the principle of conservation. Gifford Pinchot, the head of the U.S. Forest Service, publicly criticized Ballinger, leading to his dismissal by Taft.
This event damaged Taft's reputation as a conservationist and widened the rift between him and his predecessor, Theodore Roosevelt.