Which regulatory body was strengthened under Theodore Roosevelt to support progressive reforms?

The Interstate Commerce Commission (ICC) was indeed the regulatory body that was strengthened under Theodore Roosevelt to support progressive reforms. Established in 1887, the ICC was initially tasked with regulating railroads and their unfair practices. During Roosevelt's presidency, the commission was granted more authority and resources to oversee and regulate the railroad industry more effectively. This enabled the ICC to address issues such as rate discrepancies and monopolistic practices that harmed consumers and smaller businesses.

Roosevelt's administration was characterized by a commitment to combating corporate abuse and promoting fairness in the marketplace, aligning with the broader progressive movement of the early 20th century. Strengthening the ICC was part of this commitment, allowing for more rigorous enforcement of regulations that aimed to protect the public interest against powerful corporate entities.

The other regulatory bodies listed, such as the Federal Trade Commission, were established later, after Roosevelt's presidency, and were not directly strengthened during his administration. The Power Regulation Board and Transportation Industry Commission are not recognized regulatory bodies from that period and do not align with the progressive reforms associated with Roosevelt's agenda.