The car, which President Trump acquired in March to show his support for Elon Musk, is one of the first tangible casualties of their shattered alliance.
The sudden fallout ended a nearly yearlong partnership, during which Mr. Musk helped propel Mr. Trump to the White House and became one of the president’s top advisers.
The U.S. Coast Guard said it would allow the fire to burn because the cars’ lithium-ion batteries could explode. The ship’s crew escaped on a lifeboat.