At some point, a progressive president is going to declare a state of emergency due to something like climate change. In anticipation of that, Trump should use that power first, and definitely declare illegal immigration and human trafficking to be a state of emergency. There are several likely outcomes:
1) The anti-trumpers freak out, and succeed in stopping Trump, having his declaration halted by the courts or impeachment or whatever. That would be a victory for me, in that the powers of the presidency are clearly limited, and a future progressive president would presumably be similarly limited by the precedent.
2) Trump wins, and POTUS is declared/allowed to use such emergency powers. That is a loss for me (a constitutional process guy), BUT, since a progressive president would win that battle if Trump can win it, then that means that the future progressive president was going to do something like that anyway (it is inevitable), so at least in the meantime Trump does some good with the unfortunately broadly expanding powers of the presidency.
Trump needs to press to expand the presidential powers as much as possible, inch by inch to establish as much anti-POTUS precedent as possible. Everytime the anti-Trumpers shut him down, I will be happy, because the POTUS powers will become more limited. It will be easier to stop Trump than it will be to stop the future progressive/socialist president, and good precedent will be thereby established.
Granted, the Left will likely just argue that Trump is a singular president, which warranted special limits, and their more reasonable socialist president warrants special powers. But, it will at least be a little harder for them to argue that after going all out against Trump.