the satire in the original photo was misplaced

Perhaps you're not aware of the concept of synecdoche,, where one part of something is used as a representative of the thing as a whole. You saw the float and said that it had nothing to do with trump (vaguely true despite the fact that many of his party still answer his beck and call), whereas the float has "republikaner" written on it, which despite not speaking German I can only assume means "republican". So basically the float is depicting the republican party at large killing Ukraine, despite the fact that there are only two people shown.