Nothing to negotiate. Law and funding has already been passed and signed into law.
Start rounding them up, sending them south and get the wall built.
Absolutely no further authority needed.
GIT ER DONE!
Yes a lot of the problems can be cleaned up without legislation but $12 billion for the wall Trump wants to build would have to be passed. But in reality what is the Congress going to do say no? If Trump wins in a landslide he has a mandate and Congress ignores it at their peril.