out on chuck and nancy. i calmly said if you re not going to give us strong borders, bye-bye. reporter: it made headlines. even in france. it s one thing for n sync to sing it. bye, bye, bye reporter: or ann-margret to belt it out. bye-bye, birdie but this is potus and not an snl skit about a mean airline. bye-bye. did you not understand the buh or the bye? bye-bye. reporter: often his line is accompanied by a signature hand wave. if they said no i would have said bye-bye. reporter: whether it s about dealing with iran or nato. if they don t pay, bye-bye. bye-bye. bye-bye. reporter: he loves saying it to protesters. bye! go home to mommy.