If the US budget was cut in half there would be a West Russia today.
The US military budget (USD 877 bn) is larger than those of the next ten militaries put together (USD 849 bn). Also three of those ten (UK, Germany and France) are NATO members, and another three (Japan, S Korea and Ukraine) are all-weather allies. If the US decided to cut its military budget by 50%, it would still have a larger budget than the next two (China and Russia) combined.