Within days of the April 2 announcement of the tentative agreement to curb Iran’s nuclear-weapons program, it was apparent that there are substantial misunderstandings about a deal the administration has hailed as “an historic understanding.” Clearly, much work must be done if there is to be a final agreement by the June 30 deadline.

Iranian leaders quickly disputed key points about the White House’s description of the terms of the agreement. Among them was Iran’s demand that all sanctions be removed once a final deal is signed. That is a far cry from the U.S. understanding that sanctions will only be removed over time, as Iran meets its obligations. This different Iranian position may have been aimed at Iran’s domestic audience. But if Iran holds to it, there should be no final agreement.

Arms-control negotiations are rarely easy, and there remain serious questions about more than the phasing out of sanctions. These include verification mechanisms (including access to Iran’s military bases for inspections); the “snapback” provisions for reapplying sanctions; and Iran’s refusal so far to provide historical information about its nuclear-enrichment program so that there is a baseline against which to measure any future enrichment. The proposed snapback and verification provisions, while still being negotiated, look like they will be particularly bureaucratic and cumbersome.

Experience shows Iran cannot be trusted, and so those four weaknesses need to be addressed and fixed. Yes, it would be good if we could have a verifiable agreement extending the current “breakout” period for Iran to acquire nuclear weapons to one year from the current two-to-three months. And for that extension to last at least 10 years.

As things now stand, however, if in the end there is no final agreement—and if the U.S. is seen to be the reason why—we could be in a worse position than we are today, because the United Nations and European Union sanctions would likely be watered down or dropped. The U.S. would then be left with the option of only unilateral sanctions, which are far less effective. So it is critical that the U.S. position on these issues be supported by most, if not all, of the other members of the P5+1 group, as the permanent members of the U.N. Security Council plus Germany are called.