Yeah, what a weak defense.
Ukraine didn't know the military aid was being held up so no q pro q. Except for the fact that even I knew the aid was being withheld, and it was pretty explicitly going to be released when Zelensky started investigating Trump's rivals. testimony so far is that military aid, a WH visit, and basically any show of US support for Ukraine was conditioned upon damaging DEMS for Trump's political fortunes.
The House Dems are smart to gather info, record Trump obstructionism, and let public opinion turn against Trump as the facts leak out. When they have a pretty airtight case and the public understands the putrid Trump corruption, then it will be hard for GOP senators to vote against impeachment. And it will be used against them.
I'm wondering if any of the diplomats whose notes and records are being secreted by the State Dept will just reach a point where they either resign or just say F- It and provide their material directly to the legit House investigation in defiance of the State Dept. That's one possible scenario.