I think you're thinking short term. I don't think Russia cares democrat or republican, they want exactly what's happening - lack of confidence in the election process. Trump benefitted because he's reading from the same playbook - push a lack of confidence in the election process.

From Russia's standpoint, they can't take down the US. The US can certainly destroy itself from the inside though.

If we assume the GOP is already questioning all election results, then this most recent comment from Russia will bring more of the left in to question the results. When everyone questions the results, the US has a big problem.