John Kerry just gave a stirring defense of the Iran deal - but left open some major questions

US Secretary of State John Kerry spoke at Reuters' New York headquarters on Tuesday, presenting a passionately argued case in favor of the nuclear agreement with Iran, the landmark accord that Congress will vote on in a little more than a month.

At the talk, which Business Insider attended, Kerry argued that congressional rejection of the deal - which will only occur in the still highly unlikely event that deal opponents can muster a two-thirds majority of both chambers of Congress needed to override a presidential veto - would force the US to impose sanctions on the banks and businesses of signatory nations that had accepted the nuclear accord. He said it would potentially jeopardize the US dollar's primacy as the world's reserve currency.

Kerry said that Iran would have to build a "second, separate fuel cycle" to cheat on the deal, but that the agreement's safeguards make it impossible for Tehran to go that route without international monitors knowing about it. And he warned that spurning the deal could be a serious enough breach of faith to put Iran on the fast-track to a nuclear weapon.

These are standard defenses of the agreement by now. But Kerry had a few other, more notable statements about President Barack Obama's top foreign-policy priority. Here are three of the highlights.

Kerry said Iran doesn't want to build a nuclear weapon because of a religious injunction from Ayatollah Ali Khamenei banning nuclear weapons.

"The Ayatollah has issued a fatwa .... declaring no one should ever possess a nuclear weapon in Iran," Kerry said. "We said, let's take the fatwa and codify it into the agreement," in the form of the deal's permanent prohibition on Iran ever developing or even working towards a nuclear weapons capability.

This is a curious line of defense for the agreement, as the fatwa has been a frequent subject of controversy. There is no publicly available text of the fatwa and the Iranian government has superseded earlier fatwas on chemical-weapons possession and development in the 1980s. Observers disagree on whether the supposed 2005 fatwa actually exists, and what its status would be within Iranian strategic planning if it did. The Washington Post once described the fatwa as "a diplomatic MacGuffin - something that gives the Americans a reason to begin to trust the Iranians and the Iranians a reason to make a deal."

Even Kerry seemed to realize the tension in using the fatwa to sell the deal.

"The IRGC [Iranian Revolutionary Guards Corps] still wants [a nuclear weapon] and they are opposed to this agreement," Kerry said.

By implication, Kerry doesn't seem to the think that the IRGC considers the fatwa (assuming it is still operative or even exists) to be binding upon it - worrying, since the IRGC has extensive connections to Iran's nuclear program.

Violations of the arms embargo aren't binding on the nuclear agreement's "snapback" provisions - even though the embargo will be lifted as a result of the deal.

"The arms embargo is not tied to the snapback; it is tied to a separate set of obligations," Kerry said. "So [Iran] is not in material breach of the nuclear agreement for violating the arms piece of it."

Kerry is presenting conventional arms control and nuclear regulations as existing on separate-but-related tracks within the agreement. This makes sense - after all it would be illogical for an agreement meant to stanch the spread of nuclear arms to hinge on the matters related to the spread of conventional arms, many of which are widely available anyway.

At the same time, Kerry's statement beckons the question of why the arms embargo, which will be lifted eight years into the deal, was included in the agreement at all.

The arms embargo isn't strictly related to Iran's nuclear program. Kerry's answer hints at the awkwardness of linking the embargo to the nuclear issue - and then proceeding as if the two are totally unrelated.

This dynamic likely works to Iran's benefit. Tehran is already a serial violator of weapons-exports restrictions, facilitating transfers to the regime of Syrian President Bashar al-Assad and to the Lebanese terrorist group Hezbollah in defiance of multiple UN resolutions. And the US secretary of state has now acknowledged that kind of behavior won't trigger snapback, even though Iran will reap a substantial conventional-arms benefit as a result of the deal.

Brendan Smialowski/Pool/Reuters

US Secretary of State John Kerry (L) sits across from Iranian Foreign Minister Javad Zarif (R) as negotiators wait for a meeting at the Beau Rivage Palace Hotel March 27, 2015 in Lausanne.

Still no answer on the "Additional Protocol."

Kerry rightly said that Iran's agreement to work out an Additional Protocol (AP) with the International Atomic Energy Agency was one of the strengths of the deal. An AP is a country-specific set of nuclear limitations that is considered binding under international law.

"Iran has agreed to adopt, ratify, and live by the Additional Protocol," Kerry said. But the agreement text refers to "provisional" implementation of the AP, and gives no timeline for Iran to actually ratify it.

One of the mysteries of the deal is how long the US and its allies will tolerate Iran's non-binding implementation of one of the most important aspects of the nuclear deal. It's hardly an abstract question: Iran accepted an AP in 2003 without ratifying one, and then suspended implementation in 2005 on the basis that they were accepting what Tehran believed to be unnecessary and voluntary limits on their program.

Whether there's a limit to the US and its partners acceptance of provisional implementation of the AP is one of the most important questions related to the deal moving forward. Kerry talked about the AP without directly addressing it.