They can't not let you in if you're a U.S. citizen. They can search or impound your property, and they can temporarily detain you, but ultimately they have the

They can't not let you in if you're a U.S. citizen. They can search or impound your property, and they can temporarily detain you, but ultimately they have the choice of letting you in or arresting you based on some probable cause. As a U.S. citizen, sending you back is not an option.