Related, if trump is summarily deporting citizens under his new mass deportation regime, citizenship and an ability to appeal to the law isn’t going to get people back in the country. The executive runs border security
Also, CBP regards major waterways as "borders" if they terminate in an body of water that has a national border (like, say, an ocean, or Lake Ontario). So e.g. they have been known to assert the right to warrantless search within 100 miles of the Mississippi.