The fun thing about an impenetrable dome is that it is massively destabilizing and encourages a giant arms race.
When there is a credible belief that your missiles will be intercepted, you start research on defeating that system.
You either start building enough missiles to overwhelm it, and/or start research into hypersonics, space based weapons, etc etc.
This is because when someone is behind a national ABM system, that nation also starts to believe it can conduct a first strike and survive retaliation.
“space based weapons”
similar to a Tungsten Spear?
Or Nuke em from space?