Since Russia launched its full-scale invasion of Ukraine in February 2022, the United States has provided Kyiv with extensive military aid. But that aid has long been subject to restrictions. Some have to do with the type of equipment provided, such as limits on transfers of long-range missiles or aircraft. Others constrain how U.S. weapons can be used. Washington has designed many of these restrictions to limit Ukraine’s ability to hit targets far behind the front, fearing that deep strikes would be unduly escalatory. That position has been controversial. Both Ukrainian officials and outside critics argue that the Biden administration...