Hows do you stop this? Sink every boat in that town’s harbor. Repeat as necessary.
Article 1, Sect. 8. The Congress shall have power:It doesn't say Barry gets a veto here, although Harry might be a problem. And Leiberman might bring enough friends to overcome Harry. The new House should at least try doing something here, in keeping with their apparent strategy of at least trying to win the agenda, even where they can't win the results. We don't need to declare war and I'd caution against employing the "Letters" option until significant public education were done; naive public opinion would be strongly (and incorrectly) against it and we need public support on bigger issues. But some Constitutional renewing of traditional piracy related laws would be a public opinion winner.
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To define and punish piracies and felonies committed on the high seas, and offences against the law of nations;
To declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water;
When its finally time to physically move on the pirates consider going after their logistical weakness, their khat supply. My understanding is most of the Somali fighters and pirates are addicted to that stimulant, but that the plant doesn't grow in Somalia. It's openly imported and only has a few day shelf life. Blocking that, at least temporarily, may be a simple, low risk exercise. The possibility of attacking while most of the enemy goes through drug withdrawal deserves at least a little Pentagon analysis. You might just get low rankers attacking their warlord drug suppliers in search of another fix.