“Trump has offered amnesty to the 800,000 or so dreamers.”
No, he has not.
Perhaps not directly, however, that is what he is suggesting. However, he is leaving it up to Congress to make the determination and they have 6 months in which to act. Of course I think like the rest of us, he has lost faith in Congress being able to get anything done. So deportation will kick into affect, because he knows that only Congress can make laws regarding immigration. Therefore as President he is only following the power as set forth in the Constitution, and obeying the law as set forth by Congress.