The margin of error for polls six months out from election, if memory serves, is about 14%.
I think people are phrasing this wrong: it’s not that the polls are worthless, it’s that it does not tell you what’s going to happen on Election Day in any real sense. They’re useful for watching trends and gauging short term changes and impact. They are useful for telling you how things are going. They do not tell you anything remotely useful about how things will be.