It is big news, and it's not old ground.
The difference being that this was a donation to her Presidential campaign, not her Senatorial campaign, thus being unrelated to his business enterprises, and secondly this was in 2008, well into Trump's claimed conversion to the Republican party.
Lastly, this donation occurred in the same year in which he publicly endorsed McCain.
Nope. Those donations have been public record since 2008, and they've been discussed for months. And the same explanation still holds; businesses often make donations to members of both parties, and often to competitors in the same race.
It's called dividing your bets. Nothing new.