Maybe, but I suspect he's being blackmailed. Not only by the Ukraine, but China too.
Why else would he put a halt to the investigation into Burisma?
I think you're right. I think that's common practice in DC. If not, one is hard-pressed to explain Pelosi's rise to power. I suspect her husband collected blackmail information through his business dealings and availed that info to her. She did nothing of note to warrant the Speaker position. Once in power, she used that power to pay him back. Example: The only exception to Federal Minimum Wage laws is American Samoa. Guess who owns a large position in a tuna-packing factory there?