What Was the Purpose of Extorting Zelensky?

I have made a similar point already on Twitter, but it tends to get lost. So I wanted to write it up in a short post, also because the argument is too involved for a few tweets:

My simple question is: What was the purpose of Trump’s phone call with Zelensky on July 25? I would include in this the run-up to the call and events that came afterwards. And I mean the part here about investigating the Bidens. The consensus answer is: Trump wanted to force Zelensky and his government to meddle in the 2020 general election. I don’t object to that in a broad sense. But what exactly was the plot supposed to achieve?

Stories about Hunter Biden on the board of Burisma and claims that Joe Biden interfered on his behalf in Ukraine have been spun for years. This seems to be part of GOP oppo research and obviously it would be useful to turn it into the “Hillary’s emails” for 2020. If Ukraine had announced investigations into this, it would have lent credibility to such accusations, especially if Zelensky had gone on Fareed Zakaria’s show and broadcast it to an American audience.

However, here is the problem. All this was supposed to happen in September 2019, a full year before the general election and long before it was a done deal that Joe Biden would be the nominee. There might be reasons for this. For example, something might have boiled over in the background. So there was time pressure and you would have wanted Zelensky and the Ukrainian government to go through with it now. Or you wanted to…