A lot of people are working on this. There are systems that try to do fact-checking, but they're not perfected yet. I think that today, we have to depend on human beings to do this.
But this is the kind of research we should be funding. States, together, should invest in developing artificial intelligence in such a way that it is beneficial to democracy rather than harmful. But it's not necessarily profitable, so it should probably be up to governments to build a defence system against attacks from evil actors using artificial intelligence.