If Denmark chose to weaponize Maersk, they have several theoretical avenues:
Port & Logistics Shutdown: Maersk handles an estimated 15–20% of all containerized imports into the U.S. If the Danish government ordered Maersk to cease calls to U.S. ports, it would cause immediate supply chain chaos, leading to shortages of consumer electronics, retail goods, and industrial components.
Military Logistics: Through its subsidiary Maersk Line, Limited (MLL), Maersk is a primary logistics provider for the U.S. Department of Defense. It operates U.S.-flagged ships that transport military equipment globally. A withdrawal would severely hamper U.S. military mobility.