"However, you don't have evidence that counter his claims, either, so I'm not so sure that we can be so dismissive of that claim"

That's not how it works. The burden is on the person making the claim.

The basic claim being made here is that three states (which previously had gone for Republican candidates) were won by a small margin and "should" have gone to Hillary...and Russian FB ads.

This is all circumstantial evidence and weak evidence at that.

Democrats are trying to hang their hat on "Russian meddling (or "interference")". But the plain simple truth is probably that Hillary was such a terrible option that she lost to another terrible option.