Often I'll see comments like that made concerning kissing up to someone excessively. Like, a comment made about someone who is being overly flattering might be something like "wow, could you blow that guy any harder?" The implication being that the other person is kissing up to them SO hard that they might as well be performing sexual favors for them in an effort to get in their good graces. Hence likening it to a form of prostitution.
That was how I took moondog's comment. That Trump was excessively kissing up to Putin.