Ask HN: What is the minimum military spending that would keep the USA safe?

Currently the 2 largest rivals are Russia and China, and their spending totals about $300 Billion. Our budget is $600 Billion. If we have superior efficiency and weapons technology, is it reasonable to state that we could lower our spending to about $300 Billion and still have an adequate deterrent against aggression?

Is it likely that a de-escalation of spending on our side may cause decreased spending by rivals?