John Limbert belongs to an exclusive club — the 52 American diplomats held hostage by Iran for 444 days during the 1979 Islamic Revolution. Since that crisis, which began 40 years ago next month, the two countries shared an enmity that has only grown worse under President Trump.

Secretary of State Mike Pompeo raised the rhetorical stakes earlier this month when he urged the world to isolate Iran and promised to “expel every last Iranian boot” from Syria. The United States and Iran are so hostile one wonders whether they will be enemies forever.

“I’ve thought about that a lot,” Mr. Limbert said in an interview. At 75, he remains fond of Iran and committed to helping Americans understand the country, but he finds the bilateral dynamic more dangerous than ever. “I think the best we can hope for is not to get into a war,” he said, setting a low if tragically realistic bar.

In theory, no Islamic country is better positioned than Iran to play a leading role in the Middle East, because of its location, its wealth and the sophistication of its people. But that potential has been stunted because of Iran’s continued meddling in Syria, Yemen, Iraq and Lebanon, and an antipathy for the United States that is mutual and obsessive.