I think that the author of a recent letter to editor misunderstands the term “baseless.” If someone claims that Big Foot lives in the forest in Eastern Oregon, I would say that the claim is baseless since there is no evidence that Big Foot lives in Oregon (or anywhere else, for that matter). I don’t need to “prove” my assertion, especially since it is not possible prove a negative. Rather, the person making the claim must provide the proof.
So, when a newspaper says that the claims of wide spread voter fraud are “baseless” they are just saying that no credible evidence of fraud has been found — evidence that would hold up in court, not wild conspiracy theories on the web. As long as there is no such proof, the news media can quite rightly say that the claims are baseless.