IRAN HAS complied with the principal terms of the nuclear agreement reached last summer, mothballing much of the infrastructure that could be used for weapons production and shipping enriched uranium out of the country. It also has aggressively exploited loopholes in the agreement and tried to create new ones. Most seriously, it has repeatedly tested ballistic missiles that could be used for carrying nuclear warheads, even though a U.N. Security Council resolution approved in tandem with the nuclear accord explicitly called on Iran not to engage in such activity.

Tehran’s behavior comes as no surprise to the many observers who predicted the deal would not alter its hostility to the West or its defiance of international norms. Unfortunately, the Obama administration’s response has also been much as critics predicted: It has done its best to play down Iran’s violations and avoid any conflict out of fear that the regime might walk away from a centerpiece of President Obama’s legacy.

The missile tests are one example of U.S. waffling. The administration has described them as a violation of U.N. Resolution 2231 and responded with mostly symbolic sanctions of several individuals and companies associated with the program. But it has appeared to yield to Russia’s contention that Iran did not, technically, breach the resolution because it was only “called upon,” not ordered, to stop testing. A letter sent by the United States, Britain, France and Germany to the Security Council last week described the tests as “inconsistent with” the resolution, rather than a violation that would mandate enforcement action.

Another area of potential accommodation concerns dollar transactions linked to Iran. U.S. sanctions tied to terrorism and human rights still prohibit Iranian access to the U.S. financial system. Iranian officials are complaining that they have been unable to draw on newly unfrozen assets elsewhere in the world, or make trade deals, because international banks are afraid to conduct any transactions in U.S. dollars. The administration is considering issuing a clarification to foreign banks that they can conduct dollar exchanges linked to Iran’s assets or future trade deals under certain conditions.

Administration officials say the action may be needed to comply with the spirit of the nuclear deal, which promised Iran access to its frozen assets and the resumption of international trade. Secretary of State John F. Kerry, the accord’s architect, said Tuesday that the regime “deserves the benefits of the deal they struck.” There’s logic to that. But there’s also a problem of reciprocity: Should the United States take steps not strictly mandated by the text of the nuclear accord at a time when Iran is testing nuclear-capable missiles?

Not surprisingly, Republican opponents of the nuclear deal are lining up to block the administration’s prospective action; legislation is being introduced by Sens. Mark Kirk (Ill.) and Marco Rubio (Fla.). A better response would resemble that being discussed by the Senate Foreign Relations Committee’s chairman, Bob Corker (R-Tenn.), and ranking Democrat, Ben Cardin (Md.), though action is not likely before the U.S. election. They would mandate sanctions against all Iranian entities, including financial institutions, connected to the missile program and renew the broader Iran Sanctions Act. That would allow the nuclear accord to go forward, while sending Iran the message that its infractions will be costly.