Presumably, those have influenced elections, though I guess it depends what you count as an attack.
Plenty of bots try to modify public opinion. Someone hacked the DNC in 2015/16, the result of which also alleged attempted manipulation in 2008:
https://en.wikipedia.org/wiki/Democratic_National_Committee_...
Since we (as old Rummy said) do not know what we do not know, we cannot be certain about the extent of cyber attacks and what they might have influenced, and may not know these things until discoveries decades later, if ever.
Note the RNC was also hacked but the data was not leaked. Presumably used to influence the election and policies in other ways.
Yes... they might have influenced elections and now, as a result, the world must cope with the Trump regime.
Let's now fool ourselves.... Trump is probably the best, most successful attempt at world de-stabilisation all those rogue states ever achieved.
All of that applies equally to PRISM and any internal propaganda campaigns that was feeding into, no?