A pretty clear bright line is when it involves tampering with federal elections.
Tampering how? The Ukrainian ambassador, presumably with approval of his government, took an anti-Trump position in 2016 and wrote an op ed about that. Is that tampering with an election? The Russians support the anti-fracking political position here. Is that indirect tampering in favor of candidates who hold similar views? There has been some comment about attacks Russians and other foreigners have made on our online systems, which attacks are unsuccessful. Is that tampering?
I agree that tampering with vote counts is serious business. There is no evidence of foreign entities doing that, but there is some evidence that domestic political operatives have.
Putting this into the context of abuse of power, Schiff, Nadler, and maybe other Democrats have already cast a shadow over the 2020 election setting the stage for claiming that the 2020 results can’t be trusted if Trump wins. Is that tampering? I’d say yes. Is that an abuse of their power. Again, yes. As far as Trump and Ukraine is concerned, all the facts supporting 2020 tampering allegations didn’t happen and are now moot. Nothing new has been shown. So far no tampering.