It’s not so much that they think it should be over. They think it is over.
To expand a bit, I think we can assume that Trump’s support comes first and foremost from voters’ preference for him over the alternatives. And Kasich and Cruz have long been essentially niche candidates. They’re just the last ones left. When you add that to their seeming inability to win, you’ve got at least a bit of an explanation for Trump’s rising support.
