God, some of the things i've seen in this thread make my head spin. Stay in school, kids.
The Donald J. Trump phenomenon is an amalgram of several currents and themes brewing over the past twenty or so years that combined in a sort-of perfect storm to form Trump the presidential candidate and his message. Twentyish years of bad trade policies (NAFTA, etc), from both parties shipped jobs overseas, gutted unions and worker's rights, and in general hurt the middle class and helped the wealthiest fraction of Americans amass a ridiculous and disproportionate amount of wealth and power. Sprinkle in George Bush's train wreck of a presidency - 9/11, failed interventions in Iraq and Afghanistan, and the Subprime Mortage crisis and global recession, and now you have even more vitriol towards the government and the "system" at large. Then add a dash of latent racial hatred and bigotry the GOP has manipulated for years towards primarily blacks, muslims, Mexicans, and Barack Obama, and the lowered accepted discourse towards the aforementioned President and racial groups, and you conveniently have a boogieman that angry, disenfranchised, rural, largely uneducated conservative white voters can tear into over their plight the last few years. Then add in an egomaniac, with a flair for the dramatic and a mastery of media and image, and Ta-da! Boom! you have a supposed savior to fight for the angry, disenfranchised white voters who lost jobs to "lazy" Mexicans, were victimized politically, socially, and culturally by the muslim socialist Obummer, his socialist agenda and his Obamacare, and had their very existence as good Christians threatened by Muslim extremists half a world away.
Now that I gave some context for how Donald Trump could come about in this day and age, everything I just said is a myth. Donald Trump is not a serious politician and should not be treated as such. He is not a very successful businessman, he has no serious economic plan or foreign policy agenda beyond the idiotic wall and the forced deportation of members of an entire religion. His image is a farce, constructed around logical fallacies, misinformation, bigotry and xenophobia. The media has fallen for it, hook, line, and sinker, because his outlandish and incendiary comments generate press and buzz, mouse clicks, read articles, and most importantly ratings, and that's the only reason he's been tolerated thus far. He's become the frontrunner by fanning the flames of racial mistrust, bigotry and hatred, and drowned out the slightly more reasonable voices in the Republican party, compared to his. He targets the uneducated and as previously stated, he preys on victims of economic disenfranchisement and says the idiotic things people usually have the decency to not say. His movement is little more than a parasitic growth off of the Republican party, not unlike the Bull Moose party before it, and even the Republican Party itself shooting off from the Whig Party in the 19th Century.
On top of all of that, Trump polls horribly within his own party, with every major voting group, with most sane people in general (As Ivysaur astutely pointed out) and polls pretty far behind in a general election against a seasoned Democratic opponent. Sanders and Clinton both beat him, Nate Silver's and other's electoral college forecasts predict a result even greater than Obama's crushing of John McCain in 2008 - 374 votes to 164 or so, with every swing state from '08 and '12 going blue like before, in addition to Arizona, New Mexico, and even Georgia, traditional red states, projecting voting Democrat in '16, which would be almost unprecedented. It would be, simply put, one of the worst electoral defeats in American political history. He would get annihilated.
So the sooner people realize he's not what people think he is, once they realize this campaign is a farce, a PR stunt gone horrible awry, and an embarrassment to our electoral system, the happier we'll all be.