Also, for over a year now, Trump has made sure he's in the news every single day, even if it takes a more-outrageous-than-the-last tweet or public statement.
Originally, I thought these were disconnected phenomena: the first was because he has magic Teflon pixie dust, and the second was an expression of his desperate need to hear his name, and perhaps an ultimate goal of not the White House but 120% name recognition in every country in the world, to further his business (which, for the past ten years, has been not buying and selling real estate but buying nothing and selling the Trump name; see Newsweek article).
On further reflection, however, I think the second phenomenon is a conscious strategy to bring about the first -- a sort of immunization.
Consider this: if you needed to complete the sentence "Hillary Rodham Clinton is unfit to be President because...", there would be three or four things to fill in: servergate, Benghazi, the Clinton Foundation while she was Secretary of State. (You might not know much about the specifics of these scandals, or whether she actually did anything wrong in any of them, but you know they were scandals associated with her.) Lots of other things have been thrown at her over the past thirty years, but those are the ones people have mentioned in recent months, and almost the only things Matt Lauer could think of to ask about in the recent "Commander In Chief Forum". It's a relatively simple story line: "Hillary is corrupt and can't be trusted because X, Y, and Z."
OTOH, if you needed to complete the sentence "Donald Trump is unfit to be President because...", where would you start? It's like asking "Is there a good place to eat in New York City?" Things Donald said 50 weeks ago that should have disqualified him have long since been forgotten in light of things he said 49 weeks ago, which have already been forgotten in light of... you get the idea. And since there are no one or two problems that stand above the rest, the cognitively simple story is there's no one or two problems, full stop. The human mind cannot grasp such a YUUUGE collection of outrageous statements and actions, so it's left with only a vague cloud of outrage. And Trump supporters can easily dismiss each weekly expression of outrage from his opponents by saying, correctly, "Yeah, that's what they say EVERY week. The elites keep trying to tear him down, trying something different every week."
Trump benefited, of course, from running in a huge Republican primary. Everybody hated him, but there was never one clear alternative to him. He concentrated his early efforts on Jeb, his closest competitor for name recognition, then went after the other relatively-sane candidates one by one until he was left with only the equally-despised Ted Cruz as competition.
There may be something analogous -- not with other candidates but with issues and opposing groups -- going on now. Trump says A, which outrages group X. The next day he says B, which outrages group Y. The next day he says C, which outrages group Z. And so on through several alphabets. The result is a whole lot of groups of people, each with their own reason to be outraged and offended, but no single, clear story about why he shouldn't be President; instead, he can paint himself as the noble stag beset by lots of little hunting dogs.
He really is a master of the mass media, and this election is a win-win for him. If he doesn't win the Presidency, he'll make enormous amounts of money by selling his now-even-more-valuable name. If he does win, he'll leave the job of actually running the country to his Vice President except when it affects his business connections, and he'll make enormous amounts of money by manipulating U.S. policy to benefit those connections.