On December 18, the same week UN experts declared that Iran’s October test launch of a medium-range ballistic missile was a violation of this summer’s nuclear deal, Washington announced the completion of an advanced missile defense facility in Romania. It is designed, among other things, to defend Europe against Tehran’s increasing missile capabilities. The step is a welcome one, but it is still insufficient. Washington, under pressure from Russia, had previously scaled back the system’s scope, thereby leaving vulnerabilities that Iran could exploit in the future.

The Romanian facility hosts an advanced missile defense system known as Aegis Ashore. While the system is not new, the concept is: it modifies the proven sea-based Aegis ballistic missile defense (BMD) system currently deployed on a handful of U.S. Navy destroyers and cruisers for use on land. The system includes the powerful AN/SPY-1 radar, SM-3 interceptor missiles, and the Aegis combat system, which combine to detect, track, and intercept short-, medium-, and intermediate-range ballistic missiles.

The SPY-1 radar can track over 100 targets simultaneously, allowing for defense against saturated missile barrages. Now, with the addition of a new capability called “launch on remote” (LOR), the SPY-1 can be linked with other ships, land-based sites, or aircraft to direct a broad network of interceptors to fire earlier than other radars normally allow.

Moreover, the new SM-3 Block IB interceptors used in the Aegis Ashore facility in Romania can engage a medium-range ballistic missile mid-course, allowing more time respond. This capability is a proven one. Last month, an Aegis Ashore test facility in Hawaii successfully tested LOR and the SM-3 Block IB missiles.

While Aegis BMD ships have been operating around the globe for some time, land-based systems provide the benefit of operating spaces larger than a ship’s hull. This translates into more missiles and more electrical power to operate stronger radars. On the down side, an immobile system like Aegis Ashore is more vulnerable to attack and cannot be redeployed quickly if needed elsewhere.

The placement of Aegis Ashore in Romania marks Phase II of the Obama administration’s plan to provide BMD to Europe – a project known as the European Phased Adaptive Approach (EPAA). Phase I went online in December 2011 with the deployment of the Navy’s Arleigh Burke-class destroyers, equipped with the Aegis BMD system (four such destroyers are permanently stationed in Spain to patrol the eastern Mediterranean and Black Sea). Phase II has added more interceptors and radars to counter larger missile salvos. The third and final phase of EPAA is slated for 2018 with the completion of an additional Aegis Ashore facility, with more capable SM-3 Block IIA missiles, in Poland.

While Europe has been increasingly concerned about Russian aggression, the EPAA plan is primary about defending against Iran. For the past two decades, Iran has invested heavily in its missile development, with its most capable missile, the Sejil-2, able reach as far as Germany. Working together, Aegis Ashore and the existing BMD ships from Phase I (as well as other NATO missile defense assets, such as European-owned Patriot and Aster 30 missiles), can capably intercept Iran’s existing short- and medium-range ballistic missiles.

But as October’s missile test indicated, Tehran is not satisfied with its current arsenal. U.S. Secretary of Defense Ashton Carter estimates that an Iranian intercontinental ballistic missiles (ICBM) could be operational in ten years. Once that occurs, the EPAA system – which is not designed to thwart ICBM attacks as it is currently planned – will be insufficient.

The EPAA’s shortcomings stem from Russian objections to a U.S. missile defense system based in Europe that would negate its nuclear deterrent. Washington had planned to position an entirely different missile shield in Poland and the Czech Republic that was better suited for ICBMs. But bowing to Russian pressure and following the intelligence community’s reassessments of the status of Iran’s ICBM development, President Obama scrapped the plan in 2009 in favor of the EPAA.

The matter is not settled, however. In 2013, the White House adjusted the EPAA plan, cutting Phase IV – which would have employed SM-3 Block IIB missiles to intercept ICBMs targeting the U.S. – because Moscow threatened to oppose further reductions on nuclear arms. Admittedly, even if the full EPAA system with Block IIB missiles had been implemented, it would have done little to counter Russian ICBMs because their trajectory towards American shores could avoid passing over Europe and stay out of range of the EPAA interceptors – unlike an ICBM coming from Iran. Still, critics charge that Washington bowed to the demands of Moscow at the expense of American security.

While the EPAA and Aegis are at the cutting edge of U.S. missile defense technology, the scaling-back of its capabilities will leave Europe and America exposed to future threats from Tehran. Particularly, as the prospect of an Iranian ICBM grows more likely, Washington may have to reconsider whether pacifying Moscow makes America and its European allies more susceptible to Iranian threats.

Patrick Megahan is a research analyst at Foundation for Defense of Democracies focusing on military affairs. He manages the website MilitaryEdge.org.