As President Obama begins his three-week push to win approval of the Iran nuclear deal, he is confronting this political reality: His strongest argument in favor of passage has also become his greatest vulnerability.

Mr. Obama has been pressing the case that the sharp limits on how much nuclear fuel Iran can hold, how many centrifuges it can spin and what kind of technology it can acquire would make it extraordinarily difficult for Iran to race for the bomb over the next 15 years.

His problem is that most of the significant constraints on Tehran’s program lapse after 15 years — and, after that, Iran is free to produce uranium on an industrial scale.

“The chief reservation I have about the agreement is the fact that in 15 years they have a highly modern and internationally legitimized enrichment capability,” said Representative Adam B. Schiff, a California Democrat who supports the accord. “And that is a bitter pill to swallow.”

Even some of the most enthusiastic backers of the agreement, reached by six world powers with Iran, say they fear Mr. Obama has oversold some of the accord’s virtues as he asserts that it would “block” all pathways to a nuclear weapon.

Read the article in full at the New York Times.