Both the FBI and CIA have publicly stated they believe the hacks came from Russia. Whether they'll release their evidence publicly remains to be seen, however, even GOP senators acknowledge it was likely Russia. We can assume they were briefed.

>"Both the FBI and CIA have publicly stated they believe the hacks came from Russia."

Let's imagine you're the President and you discover the leaks came from US citizens with ties to the DNC (e.g. DNC employees with access to emails). Would you have anything to gain from pointing the finger at foreign political actors interfering in US politics?

Imagining motives and then working backwards is, in general, a terrible way to parse the world.

How do you think journalism or police investigations would work without such approaches?

Terrible or not, it's the correct way.

It's literally the complete wrong way. You're inventing potential motivations, convincing yourself those are the motivations of the people involved, and then likely searching for evidence that proves your speculation correct.

It's not completely baseless, a former British ambassador that supposedly has close ties to WikiLeaks has suggested the information they leaked came from a DNC insider:

https://www.craigmurray.org.uk/archives/2016/10/really-reall...

With that out of the way, let's return to the earlier question, in the situation I described previously, what would be gained by blaming a foreign group for the leaks?