Impeachment is indeed a political process. The criteria for impeachment are, to me, kind of vague. Basically, Congress can fire the President for any reason it wants. It doesn’t need evidence.
I think Ms. Pelosi has been wisely managing the D base all this time. Go too fast too early, and risk looking like a vindictive party for losing the election. Go now because too many straws have been put on the camel’s back such that the D base is going to stay home in November 2020 if the D party does nothing. From now on, slow-play the impeachment process to distract the White House and let more cage doors open up for November 2020. The president should be at 30% or less in the polls at that time. Easy D win!
The drawback is that I suspect impeachment will become a common tool. The R’s will use it to distract a D president.