New Delhi, June 17 -- The interim deal between the U.S. and Iran is supposed to usher in a two-month period that would address the most divisive issue between the longtime adversaries - Tehran's nuclear program.

Preventing Iran from attaining a nuclear bomb is a key reason that President Donald Trump said he launched the war alongside Israel in February, but the tentative agreement he has trumpeted leaves little runway to negotiate the long-running sticking point. The previous nuclear pact between Iran and world powers, which Trump pulled the U.S. from in his first term, took many months to negotiate.

Few details have been publicly released about the initial deal, set to be officially signed Friday in Switzerland, but it generally calls...