The "Pelosi slurred speech" video is the standard example.
Frankly, I don't think it matters much. These things already exist, but there's been a lot more attention to their possibility than to any of the actual examples.
The electorate is highly polarized, and most people seem well into the stage where they're happy to believe anything that supports their position, regardless of whether it's objectively credible, and disbelieve anything that contradicts it. Those who are still inclined to keep an open mind have mostly learned to be highly suspicious of visual media, regardless of the source. The press has lost what standing it had as a reputable institution, and the half-assed blogging-and-social-media channel that's largely replaced it likely doesn't have much effect either.
I don't think deepfakes have the leverage to affect future elections very much. The ranks of the credulous are swollen, but it's damned difficult to get them to march in a different direction than the one they've already chosen.