It could make it more difficult for us to use Northern Iraq as a staging area to oust Saddam. It could also make things difficult for any post-Saddam democracy.
Making it more difficult for us is not the same as making it impossible for us. Unless they make it impossible for us, this action would guarentee we will come after Saddam.
It would make the post Saddam era more unstable and would mean we will be there longer.