President Theodore Roosevelt earned a reputation as a trustbuster because he

Because he wanted to test out the power of the government to break up bad trust

He used court actions to break up business monopolies

Explanation:

In the late-nineteenth century, many big businesses, like the Standard Oil, had either bought established business arrangements, or even bought their rivals, in order to effectively destroy the competition. Many companies followed the model used by Standard Oil, since they were organizing themselves as a trust in which many component corporations were controlled by a single board of directors. Roosevelt did not see all trusts as bad, but did his best to regulate all of those that he saw as bad.