President Donald Trump’s big announcement on Wednesday at the NATO summit that he will approve a license for Ukraine to produce its own Patriot missile interceptors is a significant long-term agreement, but not one that will help the country immediately.

The Patriot missile defense system is a highly effective, expensive mobile surface-to-air missile and air defense system designed to intercept ballistic missiles, cruise missiles, advanced aircraft, and other threats. Each interceptor missile alone costs a couple of million dollars, highlighting how expensive the system can be during wartime and why the United States is trying not to reduce its own stockpiles further by giving them to Ukraine.