Yes, I believe that Donald Trump will lose the election in a landslide because Trump has said inflammatory remarks about Muslims, women, hispanics and disabled people. The general election demographic is very different from a Republican primary demographic and I believe that Trump will lose very badly to Hillary Clinton in November.
While I think Donald Trump is ahead right now, I don't think that will be the case when it is time for the presidential elections this fall. I firmly believe he will do something, or say something, that will mess up his campaign and he will not be able to recover. I think he'll lose the election, or drop out before the time comes.
Most people don't like Donald Trump, but a lot of people support him very strongly, and they will mostly come out to vote because they feel so strongly about him. Americans don't usually vote in very large numbers, so most of those people who have an unfavorable view of Trump will not vote, and some will not vote for his main opponent, Hillary Clinton, either, because she is also not very popular. Therefore, I think it will be a close race between those two.
While it's clear that Trump has a large backing for his campaign, I don't believe that the term landslide victory would apply. He has managed to step on as many toes as he has supporters. If anything, he will end up with those who dislike him voting for him simply to keep Hilary out of office. Sad, but true. Lesser of two evils!