A U.S. law first enacted in the 1990s allowing Americans to sue corporations doing business in Cuba is finally being allowed to take effect. Signed by President Bill Clinton, the Libertad Act, also known as the Helms-Burton Act, was intended to strengthen the U.S. embargo on Cuba. But a waiver was granted for a section known as Title III, which allowed U.S. courts to hold companies doing business in or with Cuba liable for damages to U.S. citizens harmed by the Castro regime. Every President since Clinton continued to waive that section of the act, but just this year, President...