I firmly believe the responsibility for the despicable action, in Salisbury, can be laid at the door of the Russian State!
The act itself was carried by the GRU apparatus (Russian Military Intelligence) with the order coming from the highest levels - almost certainly Putin himself,
A case was carefully, and efficiently, constructed, by the UK authorities, and the two GRU operatives were eventually identified.
Nevertheless, IMO those who have followed the news about the event, like myself, might well be surprised at what appears to be a certain level of incompetence on the part of the GRU.
I'm not going into details, but I believe the action could have ben carried out with a great deal more subtlety.
It could well be argued the nature of the action was a deliberate ploy, by the Russians, to make clear to the West the strength of their power, and their contempt for the likely weakness of any response.
They were surprised, however, by the support The UK received from Western allies, and especially the US. This response, apparently, was against the wishes of Trump.
The only way to stop the Russians is to make clear to them any further actions, of this type, will cost them more than any perceived benefit they gain.
If they carry on they should be identified as a "rogue" state.
NB. According to Wikipedia the GRU was founded in 1921. I understand the department was particularly active during the time of Josef Stalin.