A spate of oddball health problems afflicting U.S. diplomats in Havana is threatening to scuttle the hard-won warming of U.S.-Cuba relations under President Barack Obama, which we believe would be a tragic mistake for both countries.

Secretary of State Rex Tillerson said this week closing the U.S. embassy in the Cuban capital is "under evaluation" because of the illnesses, while five Republican U.S. senators wrote a letter urging the immediate expulsion of all Cuban diplomats and closing their embassy if Cuba doesn't take "tangible action" - which they apparently don't realize it already has.

One of the five was Cuban-American anti-Castro hardliner Marco Rubio from Florida who fought Obama's rapprochement with Cuba every step of the way and now is encouraging President Donald Trump to dismantle it - a process Trump began earlier by reinstating old restrictions on travel to Cuba.

Disappointingly, another was our own John Cornyn.

The embassy, shut in 1961 after Fidel Castro took power in a 1959 revolution, was reopened two years ago when Obama and Cuban President Raul Castro re-established diplomatic relations.

But the relative peace since then is being threatened by health problems affecting 21 U.S. diplomats, thought to be victims of unexplained sonic attacks in their residences the past year.

Their afflictions ranged from hearing loss to mild brain injury. Ten diplomats from Canada, which has long had good relations with Cuba, suffered similar symptoms.

President Castro took the unprecedented step of telling the top U.S. diplomat in Havana face to face that he was mystified by the attacks, then allowing the FBI and Royal Canadian Mounted Police into Cuba to conduct their own investigations, both of which produced nothing.

What we believe is this: The Cuban government is big on surveillance, has long experience deploying listening devices and is happy for everyone, including its own citizens to believe they are being watched and listened to.

But Cuban leaders take international relations and their international image very seriously, have cultivated them assiduously to counter the long-standing U.S. trade embargo and would gain nothing by deafening U.S. or Canadian diplomats with sonic waves, assuming that's even possible.

Theories about what else could be happening abound - a rogue element in the Cuban government sabotaging Raul Castro, Russia trying to undermine U.S. policy in the same way it did our elections, Cuban listening devices gone bad are a few - but as of now all we have is speculation.

What we do know is that the letter from the five senators should be thrown in the trash where it belongs. It has the look of an ill-informed attempt to end the positive, perhaps transformative U.S.-Cuba relations forged by Obama and put our policy back in the hands of ineffective hardliners.

We suspect from his non-committal response on the matter that Tillerson understands that. Cornyn probably does, too, but as often happens with him political concerns have taken precedent over good policy.

We would urge the Cubans to make every effort to get to the bottom of this mystery and put a stop to it. Due to limited resources, they may need help, which the U.S. and Canada should offer if they haven't already.

What the U.S. should not do is close its embassy or further dismantle our opening to Cuba. After wasting more than half a century imposing a failed, but still-in-place trade embargo against the island, we simply must move forward for the betterment of both sides.