Meddling in the democratic political processes of another country
The Russian state may have hacked the computers of the Democratic party and released information which was harmful to the Democratic Presidential candidate.
The information in support of this which is viewable in the public domain is circumstantial at best.
Let’s say the Russian state did this and let’s avoid the question of whether it could have been done by Russian actors who are tolerated by the Russian state so long as they do not harm the Russian state but who do not act under the direction of the Russian state.
Then at least let’s put the discussion on a balanced footing.
The US continually interferes in the political processes of other countries. (Leaving aside the obvious point that it regularly simply invades countries to get them to bend to their will, in reality, an altogether more serious matter than playing about with some emails). On Russia; the US funds Radio Liberty – which publishes and broadcasts propaganda into Russia which is precisely designed to undermine the confidence of the Russian people in their government. Very much like the West accuses RT and Sputnik of doing.
And in terms of direct meddling. Here is video carried on a Russian news outlet (not in fact owned by the state) (and likely shot by Russian intelligence services) showing a meeting between US officials and a Russian opposition party. Imagine the furore in the British press if Labour party figures had been meeting with people from the Russian Foreign Affairs ministry. Indeed we can see the fuss around contacts between Trump’s team and the Russian Embassy.
IF the Kremlin was behind the hack of the DNC then it is quite likely that they just take the view that they are not doing anything which the US doesn’t do to them. (Putin has very clearly denied that the Russian state was involved – though this version still leaves open the possibility of non-state Russian actors).