In 1972, the US and USSR signed the Anti-Ballistic Missile Treaty which
limited defenses against ICBM’s. The Soviet Union then quietly went back on
the agreement. Now, unlike then, the US is considered ahead in the
development of missile defenses, and some people advocate that the US should
abrogate the treaty. (Perhaps they will reconsider when the USSR has finished
collapsing.)
The difference between the good guys and the bad guys is that the good guys
break their promises in public.