So Trump's defence is going to be this. There were two unconnected things going on in parallel.
1. The release of Javelins to Ukraine were contingent generally on corruption in the country.
2. Trump wanted to pursue particular evidence of corruption about Biden.
He will say the latter wasn't contingent on the former, and that anyone who said something different was dealing in hearsay.
He will point to the discussion he had with Senator Johnson denying the quid pro quo, and that he released the Javelins shortly afterwards.
Then he will say the investigation of Biden was sensible because he has evidence that Biden is planning to steal the election, and as president, he needs to ensure the election is fair.
It's bollocks, but he will hope it's enough to keep the senate onside.