Anderson had the power to stop shipping if he wanted to. At the time of the Star of the West incident, before the Charleston defenses were properly made, he could have done great damage to the guns of Fort Moultrie. However, the Charleston defenders never proved that they could effectively hit a slow moving target in broad day-light. The Star of the West was very close to making its destination (and had Anderson done his sworn duty certainly may have done so); there was the incident of the merchant sloop loaded down with ice that failed to show its colors, it was fired on by Charleston gunners until it finally found a flag and raised it and only suffered a hole in its sails; and the incident where a one of the local gun crews accidently fired a round at Fort Sumter that bounced off its wharf when they were going through gunnery practice (they didn't know it was loaded).
David