Pelosi is screwing this up, for a number of reasons:
1) Drumpf is getting the best of both worlds right now - the political benefit of accusing Democrats of doing nothing but trying to impeach him (which they're not, currently doing) and the political benefit of not being impeached and getting away with his lawless behavior.
2) Any good leader knows that dealing with a problem immediately is the only way to go. The longer you allow a rotten apple to stay in the barrel...
3) She is losing the messaging - every day she delays an impeachment inquiry is a day that the wingnuttia can spin their yarns and continue to break the law. Waiting for bipartisan or public opinion to change is stupid...that will change when you trot the crooks out in public hearings. The longer she delays, the less control of the message she has.
4) I can't figure out, for the life of me, why you would abnegate your Constitutional authority when it is literally the only thing that can be used to hold the POTUS* accountable for crimes. If you make the claim that somebody is committing crimes, then what the dumptruck are you waiting for? Yeah, we know the Senate is going to hold a kangaroo trial, if any trial is held at all, but get those traitors on the record for it. I just don't get it.
5) An impeachment inquiry doesn't have to lead to Articles of Impeachment or even a trial. It would, however, be a fantastic public arena to trot out the Mueller report to a public that isn't going to read it and who doesn't even know what it means.