Yes, we better already have one. I believe there are agreements not to militarize space, but we need to be able to militarize it on a moment’s notice.
A BFR could put up a dozen-plus 10 metric ton Rods-From-God in one launch. Think GBU-57 with impact on target at Mach 25—40.
Plasma and MHD applications from Russian AYAKS / NASA Glenn hypersonic applied to the reentry device could minimize energy lost to passage through the atmosphere. The reentry plasma can be manipulated to provide maneuvering.