"The espionage story of the year, and perhaps one of the greatest foreign operations in decades, has undoubtedly been Russia’s successful effort to influence this fall’s presidential election through hacking—penetrating Democratic National Committee servers and the e-mail account of John Podesta, Hillary Clinton’s campaign chairman."
Those are the questions you should be asking.
They may be telling the truth. They may be telling part of the truth. They may be lying.
And these are just the generic reasons. In this particular case, the first obvious question is why NSA et al. would ever state their certainty in a Russian attack publicly. There are no good outcomes. Either they are right and the Russians blow up the bridges as they retreat or they are wrong and the Russians know they are incompetent.
> I trust in DKIM signatures. Any statement by an intelligence service ever is caked in multiple layers of conflicting motivations from expanding their budget, pleasing their lax overseers, deflecting incompetence to confusing adversaries.
That is some of the motivations, the negative ones, but you fail to list all the reasons they wouldn't want to lie to make your argument sound stronger.
I understand being skeptical of an intelligence service, but all intelligence services? Well, you'd have to have a pretty strong reason to doubt.