Sally, impeachment is a done deal...for sure, without question.
Pelosi knows what she's doing. I disagree with your assessment that Pelosi is "slow walking" this. Actually, the witnesses have been coming in fast and furious including even on this past Saturday. This is moving right along at a quickened pace. The reason she doesn't just go present Articles of Impeachment right now even though it's a sure thing is:
1) The stronger and more complete the evidence, the more Republican House members will vote to impeach which in turn will likely mean more Senate Republicans voting to convict.
2) The more evidence that is brought, the larger the NUMBER of Articles of Impeachment. Democrats are in the CATBIRD SEAT (I know, because they are crowding me) right now, so they can move as quickly or as slowly as they want.
3) Timing wise, it isn't a horrible idea to have a Trump impeachment trial in the Senate in 2020 as people are pondering who to vote for. Pelosi is no dummy. She will have this all timed out as she sees fit.
4) Lets Trump twist in the wind a bit, likely leading him to say more and more unhinged things. He deserves to have to twist a bit. Somewhere there's a sweet spot regarding timing that hurts Trump the most, and it's probably not right now and probably not terribly close to election day...just in between there somewhere. That's probably the target.
In due time, Grasshopper. He will be impeached. Just wait.