The mechanism: The Jones Act (46 U.S.C. § 55102) requires that cargo moved between two U.S. points travel on ships that are U.S.-built, U.S.-flagged, U.S.-crewed, and U.S.-owned. That's the entire moat around Hawaii and Puerto Rico freight: no foreign carrier — not Maersk, not MSC, not COSCO — can legally run a ship from a mainland port to Honolulu or San Juan and back. The law is currently the subject of an actual live test. On March 17, 2026, DHS granted a limited coastwise waiver (for roughly 659 energy and fertilizer commodity categories) at the Pentagon's request, later extended to expire August 16, 2026. In early July, House Speaker Mike Johnson, Majority Leader Steve Scalise, and roughly 50 other House Republicans sent a letter urging the White House to let that waiver lapse on schedule, arguing an 11-week review found no gas-price benefit and that the suspension mainly helped foreign and Chinese-linked operators. The waiver itself doesn't touch general merchandise to Hawaii or Puerto Rico — but it's the clearest signal in decades of how much political appetite exists for opening domestic cabotage to foreign hulls, and every renewal fight normalizes the next one.