This event says a lot about both Trump and O'Donnell. First, the charity is eminently worthy (I and my wife have made separate, much smaller, contributions to it). Trump's contribution was thus to a good cause, and deserves at least some praise for that. But what were its motives - there are, after all, many very worthy charities in this world. My best guess: Trump and his campaign have been delighted with Harvard professor Laurence Tribe's appearance on Lawrence O'Donnell's show a few nights ago, excoriating Ted Cruz's hypocrisy in being not a literal originalist about the Constitution and what it says about "natural born" and American Presidents - saying it's "settled law" though it's not -when Cruz has argued throughout his career that the Constitution must otherwise be literally respected. Trump has seized on this in his speeches, trumpeting Tribe's statements as support for Trump's attack on his leading rival, Cruz.
Given that backdrop, Lawrence O'Donnell had no choice but to refuse the donation, to make sure it could not be construed as some kind of reward from Trump for the Tribe statement. The donation also shows something about Trump's thinking - rewarding people who support him has so intrinsically been the way he has done business all of his life, that it probably never occurred to him that making the donation could create an ethical problem for O'Donnell. Trump truly does play by his own rules, which is no doubt one of the main reasons he has been doing so well in the polls.
As for the natural-born issue, I've to say, being a supporter of neither Cruz or Trump, that I think the interpreation that born of an American parent should be the equivalent of born on American soil should be the rule we follow when it comes to Presidential candidates. I'd like to see the Supreme Court make a definitive ruling on this as soon as possible - which I know will need a case to be brought before it, after the case goes through the lower courts, which means it likely will be not soon at all.
In the meantime, kudos to Donald Trump for whatever part of his attempted contribution was truly charitable - and for writing the check which will indeed result in help for Malawi children, via Lawrence' O'Donnell's check which Donald Trump's check motivated - and kudos to Lawrence O'Donnell and his ethical compass for turning the original check down, and threading the needle in a way that did not disadvantage the kids in Malawi.