I think Barr is a sharp guy, but I think he's wrong on this.
First, it's only fair to point out that he did say this, which suggests he
would have found it legally invalid if they'd have charged Trump with conspiracy to subvert the electoral process:
“I think that it’s not an abuse — the Department of Justice is not acting to weaponize the department by proceeding against the president for a conspiracy to subvert the electoral process.
But I still think the whole "fraud" claim is bogus. The theory of the indictment potentially criminalize any future claims of election fraud by anyone if those claims were accompanied by efforts to change the result of an election. All it takes is to be able to convince a jury that the claims were "fraudulent". But I think that making such statements is well-within the realm of legitimate political speech/disagreements.
Even worse, I think the principle could be expanded to not just elections, but to any proceeding -- including legislative proceedings -- of the federal government. After all, the proceeding with which Trump allegedly tried to interfere was a
congressional proceeding. So if trying to influence the President of the Senate to act in a certain way is criminal if the arguments you make are deemed "fraudulent", then wouldn't the same logic apply to any legislation? Make an argument deemed "fraudulent" in an effort to influence legislation, and you could go to prison.
We can't go anywhere near that line of reasoning. Politicians -- and others -- lie about politics. And very often, people on
both sides of an issue accuse the other side of lying -- i.e., committing fraud. We cannot ever give prosecutors/juries the right to decide what kinds of political speech are permissible.