Final answer:
The muckrakers were instrumental to the progressive reform movement by exposing societal problems and galvanizing public and legislative action for change. Their journalism was a key driver in addressing issues and initiating the Progressive Era, influencing legislation and societal attitudes.
Step-by-step explanation:
The muckrakers signified much about the nature of the progressive reform movement because they exposed social injustices and spurred calls to action. They shed light on various societal problems such as corruption, poor working conditions, child labor, and unsanitary living conditions, captivating a largely White, middle-class audience. Their investigations, published in outlets like McClure's magazine, prompted Progressive activists to lobby for legislative changes aimed at addressing the issues troubling industrial America during the Gilded Age.
President Theodore Roosevelt, despite supporting progressive reforms, dubbed these journalists 'muckrakers' after a character in John Bunyan's Pilgrim's Progress, who was preoccupied with raking filth. The term initially carried a negative connotation but has since become associated with the essential role these journalists played in initiating the Progressive Era. Their work influenced Progressive legislation, encouraging everyday Americans to pressure their legislators for change.