I had missed this reporting about Trump/Zelensky but this is probably it:
But we’re reliably told that the president has a second and more venal agenda: He is attempting to force Mr. Zelensky to intervene in the 2020 U.S. presidential election by launching an investigation of the leading Democratic candidate, Joe Biden. Mr. Trump is not just soliciting Ukraine’s help with his presidential campaign; he is using U.S. military aid the country desperately needs in an attempt to extort it.
The strong-arming of Mr. Zelensky was openly reported to the New York Times last month by Mr. Trump’s personal lawyer, Rudolph W. Giuliani, who said he had met in Madrid with a close associate of the Ukrainian leader and urged that the new government restart an investigation of Mr. Biden and his son. Hunter Biden served on the board of a Ukrainian gas company, while Joe Biden, as vice president, urged the dismissal of Ukraine’s top prosecutor, who investigated the firm.
Mr. Giuliani also wants a probe of claims that revelations of payments by a Ukrainian political party to Mr. Trump’s 2016 campaign chairman, Paul Manafort, were part of a plot to wreck Mr. Trump’s candidacy. In other words, Trump associates want the Ukrainian government to prove that Ukraine improperly acted against Mr. Trump in the 2016 election; but they also want it to meddle in his favor for 2020.
https://www.washingtonpost.com/opinions/global-opinions/is-trump-strong-arming-ukraines-new-president-for-political-gain/2019/09/05/4eb239b0-cffa-11e9-8c1c-7c8ee785b855_story.html