@Jazzhead you said the National Enquirer did this as SOP and not as a favor to Trump during his election. They clearly are on the record saying otherwise.
They apparently do buy and bury stories as SOP, according the article I found and linked to on the other thread. The difference, I guess, is that they typically do this for their own benefit - by buying and burying celebrity gossip stories they gain access to the celebrity for purposes of "insider" pieces that appeal to their readership. And they (at least according to the article) did so with respect to Trump stories over the years. Here, however, Trump himself wanted a story buried for his own purposes, and contracted with the Enquirer to do the buying and burying. Instead of buying off the blackmailer directly, Trump reimbursed the National Enquirer to do so.
Is that an illegal campaign contribution? I don't know - the motivation may have been to save his campaign, or his marriage, or both.