I think the steelman for this would be something like: people hear factually incorrect assertions with enough frequency from enough different sources and become

I think the steelman for this would be something like: people hear factually incorrect assertions with enough frequency from enough different sources and become convinced that these assertions are true. This is basically of the idea of sockpuppeting/astroturfing. Given that both major political parties in the US deploy such tactics, it is not unreasonable to think that they are effective. And when these tactics are deployed by a hostile foreign power we should be even more upset than when they are used by domestic sources.