If nobody likes Hillary and Trump - then why are they leading? Somebody is voting for them.
It is an exaggeration. Trump received almost 50% of the votes in the GOP primary, and Clinton received more than 50% during the democrat primary. That means that at least 20% to 25% of the American voters support these candidates. But the truth is that, for both of them, the unfavorability rating is much more than the favorability.