Depends on how the clause it written. Probably not. And if so oh well, national security trumps business interests everytime.
Any contract providing security for a U.S port or airport should be cancellable whenever a significant change of control occurs with the originating contracting parties. Unilaterally by the US government if this somehow escapes the review of due diligence by both the buyer and seller. Our security's what is to be sold - we have an active interest.