I would say that the challenge of assigning responsibility isn't that significant. The issue is that we can't assign responsibility in the way that we're used to from a legal perspective, so beyond a reasonable doubt.
In general, our intelligence capabilities mean that we know the perpetrators of these activities, especially when it comes to Russian involvement. The Russians, by and large, don't hide their activities. On the contrary, they want us to know that their interference has caused the major chaos. Ultimately, the Russian strategy is to see the world burn.