People in vintage American convertibles pass by the U.S. Embassy in Havana. (Desmond Boylan/Associated Press)

PRESIDENT BARACK OBAMA’S much-hyped restoration of relations with Cuba was a bet that diplomatic and economic engagement would, over time, accomplish what 50 years of boycott did not: a rebirth of political freedom on the island. So far, the results have been dismal. In the two years since the U.S. Embassy in Havana reopened, repression of Cubans — measured in detentions, beatings and political prisoners — has significantly increased, while the private sector has remained stagnant. U.S. exports to Cuba have actually decreased, even as the cash-starved regime of Raúl Castro pockets millions of dollars paid by Americans in visa fees and charges at state-run hotels.

Now there’s another sinister cost to tally — the serious injuries inflicted on the U.S. diplomats dispatched to Havana. This month, the State Department announced that two Cuban embassy staff had been expelled from Washington because of “incidents” in Havana that left some American diplomats and staff members with “a variety of physical symptoms.” Anonymous sources speaking to various news organizations have since provided shocking details: At least 16 American diplomats and family members received medical treatment resulting from sonic attacks directed at the residences where they were required to live by the Cuban government. A number of Canadian diplomats were also affected.

CBS News reported that a doctor who evaluated the American and Canadian victims found conditions including mild traumatic brain injury, “with likely damage to the central nervous system.” According to CNN, two Americans evacuated to the United States were unable to return to Havana, while others cut short their tours of duty.

The State Department is saying that it has not identified the source of the attacks, though it is holding the Cuban government responsible under the Vienna Convention, which requires host governments to protect diplomatic personnel. Some news reports have passed along speculation that rogue Cuban security forces might be to blame, or perhaps a third country interested in disrupting Cuba’s rapprochement with the United States. Such theories must be weighed against facts there: Cuba is a small, highly disciplined police state where next to nothing goes unobserved by the regime — much less high-tech assaults on foreign diplomats.

In fact, the sonic attacks would be in keeping with, if an escalation of, harassment that U.S. diplomats have long suffered in Havana, including constant surveillance and home and vehicle break-ins. Instead of easing this abuse, the reopening of the embassy may have intensified it. And no, the Trump administration, which has largely preserved Mr. Obama’s opening, is not to blame: State says the attacks began in November 2016. Rather than seize on them, the State Department under Secretary of State Rex Tillerson has played them down; the Cubans were expelled in May, but no announcement was made until this month. The administration appears to be giving the Castro regime the benefit of the doubt — which, considering its overall record since the restoration of relations, may be more than it deserves.