I agree that this investigation is likely to help the president in his re-election. However, it will NOT hurt the House majority or Senate races. The Democrats had exactly zero choice.
The reason that Pelosi didn't wait for the transcript (and repeat the Mueller Report error) is that she has enough with what Trump has already agreed to.
THE CALL
The Mueller Report was issued.
The next day, Trump withheld $400M funds from the Ukraine.
A week after that, Trump called the Ukraine and asked their president 8 times to investigate the Bidens.
After the Senate insisted, he released the money.
THE WHISTLEBLOWER
The whistleblower followed the law. The IG investigated and found the information very damaging and give it to the DNI to be farwarded to the Congress, as the aw required. The WH and Justice intervened and order the DNI to withhold the document, which refers to more than on event.
CONCLUSION
These two are enough for impeachment inquiries to start
A) The president requested that Ukraine interfere with the US election by investigating the Biden's.
B) The president and Justice interfered and ordered the DNI to withhold the IG assessment.
I desperately want Trump out. But I think this is a bad idea. I don't think there's going to be a smoking gun, and I think the inquiry will end up collapsing. If Trump actually releases the transcript, you can be sure it's not going to show anything. That doesn't mean he didn't pressure them in other ways, but good luck proving it. I'd wait until you know you've got evidence of something impeachable. I'm not convinced they do.