Trump is a fool and I'm pretty in the middle and even lean conservative on some topics
the only reason he is leading polls is because the Republican pool of candidates is so weak and one dimensional. there aren't any likable personalities, and generally speaking conservative Presidential candidates have that 'family good ol boy' sort of vibe. no one like that, no one really trustworthy seeming (although I guess most politicians don't seem trustworthy)
he's also leading the polls because extreme parts of parties always are the most involved and active at the start. more middle leaning or soft Republicans of the general public could care less this early on to pay attention. its unlikely Trump maintains this popularity in the polls, it's just no one cares yet. less people with big voices are paying attention now.
even if he was likable and smart (cough at both of those), no political party is going to let a billionaire run for them as President because the general populous would never vote for someone like Trump simply due to a lack of relatability. the Republican Party will do something to hurt the Trump reputation
at any rate I agree with others that if Trump somehow did get the Republican seat in the race then it would be a landslide win for the Democrat, most likely Hilary Clinton
I know I'd rather vote for an extreme Democrat than someone like Trump, because I'd much prefer the country go in debt trying to help itself internally with social welfare then go in debt and destruction from fighting wars and not treating people on our borders kindly