Comment Well, duh... (Score 1) 332
Being at "the top" of Earth's gravity well, the moon is, sort of, the "ultimate trebuchet". Once a beachhead had been established, so to speak, with some relatively simple calculations (well, simple for the sorts of people that are capable of establishing a functioning moon base), one could simply lob largish rocks down at earth with enough precision and devastating kinetic energy to be a serious problem.
And, as far as tactical highground goes, it's profoundly defensible. One would need a very expensive and very rare, also very heavy, lifting rocket boosters to get from "the bottom" of said gravity well, to take any kind of meaningful offensive action against the installation (though the supporting ground-crew could find themsleves in a bit of a sticky situation I suppose).
That's just a simple scenario. I don't think the tactical potential of the moon has escaped anyone who gets paid to think about outlandish (but possible) wastes of tax revenue. i.e. Andrew Marshell, Director of the Defense Deparment's Office of Net Assessment.