It's been my impression that the US and Russia conduct various sorts of covert mischief such as this, but it's usually under the radar.
"Hacking" an insecure email server configured by campaign volunteers or other non-technical people is not exactly what would qualify as a "state sponsored attack".
(edit: if you disagree please explain why rather than simply downvoting)
So are you saying that the Russian government either unintentionally left a trail (IOCs) on the server, or intentionally left a trail because it wanted to be detected?
Or are you simply claiming that "Guccifer 2" is on the payroll of the Russian government?
(or some combination of the above)...
The fact that some of the leaked emails/information of from the "Guccifer" et al. hacks have also been tampered with in order to achieve a specific political goal also hints at a higher objective which isn't something one usually associates with cybercrime or even hacktivism.
Criminals would steal, sell and run and hide (not that you could hide these days if you break into a US government network), hacktivists would not usually tamper with the information they release as it goes against their own philosophy.
What tampering has occurred?
http://www.bbc.co.uk/news/technology-36913000
http://arstechnica.com/security/2016/06/guccifer-leak-of-dnc...
The emails released in 2013 also show some signs of tampering, there were incidents of duplicate headers and the times of some of the emails were strange (mostly related to Benghazi ironically) this was a copy paste error but again no one knows to what extent the "content" if and was tampered with.