Not that I'd put it past Trump's increasingly partisan and corrupt DOJ to interfere in the 2020 election by announcing a baseless investigation on either Biden: Trump has clearly sought that very thing for awhile, as we know from the Zelensky call.
But for now, this will do.
Even Ukraine didn't announce an investigation, despite being under extreme pressure from Trump's Administration to do so.
You've swallowed the party line hook, line, and sinker, but the lawyers aren't biting.
Here is further reading for you. https://www.factcheck.org/2019/09/trump-twists-facts-on-biden-and-ukraine/