"& probably summary lynchings too"
That's conjecture on your part - there is no evidence to support it.
As far as the other things are concerned, the use of waterboarding would result in a huge outcry of condemnation, and the ex-director of the CIA has publicly condemned Trumps remarks.
I think we need to understand that President Trump is under enormous pressure to meet the expectations of his supporters, so he will at least show signs of carrying out some of his 'first day' electioneering promises.
He needs the will of the American people to succeed however, and perhaps it will not be long before stark realities kick in. His Mexican wall promise would be a disaster in so many ways, even if it could be done - which I doubt.