David Hearn, a former canoeist, is accused of vandalizing the algae-challenged pool, which President Trump has said he would repair and beautify with fresh sealant. But the algae returned and the paint peeled.

The last time the park recorded 100 degrees was July 18, 2012.

Any Israeli attempt to kill Abbas Araghchi, the foreign minister, or Mohammad Ghalibaf, the Parliament speaker, would have derailed peace talks, American officials feared.