> Border guards have the power to prevent you from entering the country if they believe your business is unlawful No. The USA can never deny entry to citizens

> Border guards have the power to prevent you from entering the country if they believe your business is unlawful No. The USA can never deny entry to citizens (nor any other country). They may arrest you on the spot, but can't deny you entry. Green card holders is a different story, they have no right to enter and are at the discretion of the authorities.