That makes no sense to me at all. Dims can't impeach anyone, they are a minority. They would want a new EO to extend DACA, so why would they impeach him for doing so if they could?
Sure they would get their EO done, that's not the point. The point is to coerce Trump into doing something they can use to impeach.
This is pretty much moot if the Dims don't retake the House, but if they do, this would be one of the reasons.