I believe that to board any flight to a destination outside of US territory, a passenger is required to present his or her passport when checking in for his or her flight. That has been my experience.
Correct — my experience as well.
Now with some of the derps...using PRIVATE conveyances, maybe different.
What if someone takes a boat onto Chesapeake Bay, goes outside the 12 mile limit, reaches a yacht or freighter and poof.
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They are going to need a valid passport whenever they reach a port of entry.