Initially, Upton Sinclair was disappointed that President Roosevelt did not take action in response to the revelations in The Jungle since he did not immediately close down the meatpacking plants that were found to be unsanitary and unsafe.
However, Sinclair eventually came to appreciate the President's approach, which was to carefully investigate the allegations and then use the findings to push for legislation that would bring reforms.
Sinclair played a key role in this process by leaking the results of the Neill-Reynolds Report to the press.
This helped to build public pressure for reform and led to the passage of the Meat Inspection Act and the Pure Food and Drug Act in 1906.