This deal with Iran is a good one

It is an interim agreement, not a treaty (which means, among other things, that it doesn’t require Senate ratification). It is meant as a first step toward a comprehensive treaty to be negotiated in the next six months. More than that, it expires in six months. In other words, if Iran and the other powers can’t agree on a follow-on accord in six months, nobody is stuck with a deal that was never meant to be permanent. There is no opportunity for traps and trickery.

Meanwhile, Iran has to do the following things: halt the enrichment of all uranium above 5 percent and freeze the stockpile of uranium enriched to 3.5 percent; neutralize its stockpile of uranium that’s been enriched to 20 percent (either by diluting it to 5 percent purity or converting it to a form that cannot be used to make a weapon); stop producing, installing, or modernizing centrifuges; stop constructing more enrichment facilities; halt all activities at the Arak nuclear reactor (which has the potential to produce nuclear weapons made of plutonium); permit much wider and more intrusive measures of verification by the International Atomic Energy Agency, including daily inspections of all facilities.

Without going into a lot of technical detail (which can be read here), the point is this: The agreement makes it impossible for the Iranians to make any further progress toward making a nuclear weapon in the next six months—and, if the talks break down after that, and the Iranians decide at that point to start building a nuclear arsenal, it will take them much longer to do so.