THE LASTING foreign policy legacy of a president often doesn’t become clear until years after he leaves office. That may be particularly true of President Obama, because some of his most distinctive initiatives were, in large part, bets on long-term results. The ultimate success of the nuclear deal Mr. Obama struck with Iran — assuming it is preserved by the Trump administration — will depend on whether the Islamic regime sets aside its ambition to build nuclear weapons during the coming decade. Similarly, the president’s decision to reopen relations with Cuba without requiring any political liberalization by the Castro regime will be judged on whether greater engagement with the United States eventually helps to bring about that change.

For now, the Iran deal has at least temporarily restrained Tehran’s push for nuclear weapons, but two years of detente with Cuba have delivered almost no positive results. Repression against the political opposition has escalated even since the death of Fidel Castro, whom some had blamed for the regime’s continuing hard line. Last week the Cuban Commission on Human Rights and National Reconciliation said it had documented a total of 9,940 arbitrary detentions in 2016, the most since 2010. There were 82 long-term political prisoners in June, it said — just 18 months after the Obama administration boasted that the jails had been emptied as part of the renewal of relations.

The regime’s attacks have been focused on groups seeking a democratic opening, including the Ladies in White, who are regularly assaulted and beaten for attempting to stage peaceful assemblies, and the National Patriotic Union of Cuba, a pro-democracy organization centered in the city of Santiago that was the target of a major sweep shortly before Christmas. Danilo “El Sexto” Maldonado, an internationally renowned dissident artist, has been imprisoned since Nov. 26, when he responded to Fidel Castro’s death by painting the words “he is gone” on a wall.

The White House calculated that keeping faith with the democratic opposition was less important than opening avenues for foreign investment and trade. But there has been little progress in those areas either. U.S. exports to Cuba have shrunk, totaling only $370 million between December 2014 and October 2016, according to a report in the Miami Herald.

Obama administration officials tout the increased flow of remittances by Cuban Americans, saying they have bolstered the private sector. But since the middle of 2015, the number of self-employed Cuban workers has increased by only 7 percent — to 535,000, or less than 5 percent of the population. President Raúl Castro announced that the economy as a whole shrank by nearly 1 percent in 2016, largely because of the loss of subsidies from Venezuela. In the same speech, he reiterated that the regime was “not going, and will not go, toward capitalism.”

The absence of results may tempt a President Trump to scrap Mr. Obama’s opening. Mr. Trump should instead improve on it. A break with Havana would dash the hopes of millions of Cubans who still expect the United States to use its leverage to promote real change. Mr. Trump should freeze contacts with the regime’s security agencies and link any further U.S. economic concessions to an increase in political freedom.