I don’t see how Swift could sue West for defamation. He was incredibly rude and out of line, but I don’t think he said anything negative about her. She might have some other grounds for suing him (as metioned she could claim his interuption cost a chance to promote her music and therefore cost her money), but I didn’t see anything close to defamation.
Techinally, Obama might have a case for defamtion, except Wilson was telling the truth, when he shouted “You lie!”.
Even if Obama’s statement about illegals not being covered was true (it wasn’t), “You lie” seems way to general to be defamation, unless BHO could prove that he has never told a lie. Plus, as mentioned, he is a public figure, so the standard for defamtion is higher.
Swift suing West was not the point the author was making.