Russian industry reportedly is working overtime to modernize a new A-50 as a replacement for the first destroyed jet. The cost—potentially hundreds of millions of dollars—is significant. In the meantime, the Russians rapidly are losing their ability to control the air over southern Ukraine.

Still, it’s unlikely the Ukrainian air force can keep shooting down Russia’s best jets at the current rate. Four months after Russia-aligned Republicans began blocking U.S. aid to Ukraine, Ukraine’s stock of Patriots is “dropping to a critical level,” according to Anton Gerashchenko, a former advisor to the Ukrainian interior ministry.