Just because it shows your candidate on the defensive doesn't mean it is a garbage poll.
If I'm not mistaken, Emerson has actually been one of the more generous pollsters to Trump, along with Rasmussen. The fact that he's trailing in Emerson and Rasmussen polls should alarm anybody that supports Trump.
You also seem to somehow be taking one CNN poll from before public hearings have begun as an indication Trump will be re-elected, and I think that's a mistake. Even if it is true that just 42% support impeachment and removal in Michigan, and it stays that way, it doesn't mean Trump is popular or broadly liked, nor does it mean he is in a better position than in 2016, when he just barely squeaked by.
My advice, if you choose to take it, is to wait for more data and aggregates - we may have a clearer picture in a couple of months. This is just getting started. Support for impeachment has grown steadily, and from the looks of it, will continue to grow.
Polls at this point mean nothing too don't forget.