According to the Times, Bolton says Trump was wanting Ukraine to investigate much more than just Biden--for Trump the investigation wasn't about narrow political advantage against a rival, he was targeting corruption by multiple democrats:
"But on Bolton’s account, that isn’t what Trump was doing: the key words in the Times report are ‘Democrats’ — plural — ‘including the Bidens’."
"The plural ‘Democrats’ of the Times report on Bolton’s book are the Democrats of 2016 — the Clinton campaign and the DNC. Joe Biden’s role in the dismissal of a Ukrainian prosecutor during the Obama years also comes up in Trump’s call with Zelensky,"
https://spectator.us/john-bolton-war-trump/
This wasn't simply a matter of Trump getting Ukraine to investigate the Bidens to impact the 2020 elections.