Donald Trump owes his political viability to the cowardice of Republican politicians who keep promising one thing and delivering the opposite. Voters have watched Trump speak plain truth, as opposed to the marble-mouthed equivocations and double-speak of the Republican leadership, and they’ve seen him lose valuable business as a result. They compare his resolute defiance with Republicans who won’t even risk a committee assignment or a frown from the Washington Post, and prefer the chance, however slim, that Trump has come around to their way of thinking over the certainty that Republicans will betray them yet again.
I don't think Trump is the right candidate for president-- I think he should aim for a lower office before trying his hand at the presidency. That being said, I do find his candour refreshing, even if I'm not entirely convinced he's a genuine Republican. There are a lot of people fed up with the current leadership and they are hungry for someone who speaks to their issues and their mindset in an unequivocal fashion.