Trump is upset about his own internal polls showing he is losing. Of course, it’s a long time until the election and polls don’t mean much now.
Trump will almost certainly claimed the election was rigged if he loses. However, his claim will look weak if his totals look like the polls. For example, if he is expected to get 47% and he gets 47%, it will be hard for him to make a case that he was cheated.
However, if he is expected to get 52% (and he will find or make up a poll that says that) and he only gets 47%, he will say he was cheated.