Are you referring to flights returning to the US? If so, you have cleared SXM's security, but you haven't cleared TSA security. TSA has no control over the quality of the security check that you undergo at a foreign airport. All international travelers returning to the US must go through a TSA security checkpoint prior to entering the secure area for a connecting flight. Note that in Atlanta, due to the configuration of the airport, this used to be required even if ATL was your final destination.