Dismissing Donald Trump as a buffoon would be a mistake:
1. Donald Trump has sufficient personal assets to outspend every single presidential candidate on both sides.
2. Donald Trump because of his funds has the ability to hire enough people to make sure he is on EVERY primary ballot before the convention.
3. Donald Trump has sufficient funds to make a lot of trouble for any state level or even federal level candidate who speaks out against him.
As pointed out here, Ross Perot was an egotistical blowhard, too, "but he handed the election to Bill Clinton." Perot was running as an independent rather that seeking the GOP nomination, so the comparison isn't perfect; whatever votes he gets in the primary wouldn't have gone to Hillary the way Perot's cheated G.H.W. Bush. But if he does well enough in early states, it could chase off far better candidates. And the longer he's around (especially if he's in the debates), the worse the GOP brand will look. One clown can spoil the whole circus.