The US invests loads in new military technology, probably more than every other country put together. Their main problem isn't lack of investment, it's spending the money poorly.There may not be an arms race as such, but Russia and China are heavily investing in their military tech. Our relative lack of investment at least gives them a chance to close any gaps and, of course, numbers are also a factor. Russia is definitely expansionist and we don't seem to be taking that as seriously as we might.
- pursue "kewl" ideas that have little basis in reality,
- set unrealistic goals and when the project inevitably fails they're left with no replacement for their existing kit,
- spend everything on niche capabilities for whatever is trendy today and end up with an obsolete capability as the original problem no longer exists when the new kit finally arrives,
- duplicate efforts within their military for the sake of preserving bureaucratic empires,
- keep flogging a project horse long after it's dead because to admit failure would be fatal to someone's career progression,
The Russians and the Chinese tend to do less of this, probably because they spend far less on their militaries and so have less money to waste to begin with.
As I have mentioned above though, I am sceptical about whether the proposed nuclear powered cruise missile will be practical in the foreseeable future, so the Russians don't appear to be entirely immune from "American disease" when it comes to procurement.