I has been clear for a while that Trump has used campaign donations he receives to pay his legal expenses. I'm not sure if that's legal, but it is pretty clear that if it is illegal no one is enforcing that law against Trump.
But legalities aside, does doing that help Trump? Campaign donations from individuals are subject to donation caps. If Trump maxes out his supporters raising money for his legal fees, will he have anything left over for his actual campaign? Wouldn't it be better to just set up a legal defense fund? I'm sure his lunatic followers will donate to that too (he can call it something catchy, like "The Witch Hunt Defense Fund"), and those donations would not affect what they could donate to his campaign.