Well you just admitted it, he's been working on the Biden - Ukraine connection on behalf of a man he represents who was under investigation for the Russian Collusion narrative, as such when the ex prosecutor contacts him with information about what transpired and they also have information that it was actually Ukrainian and not Russians that was used to set up the Russia Collusion theory he has every right to talk with them and use that information in defense of his client, therefore this all started taking place before Biden announced his run so there's no quid pro quo involved here. Thank you very much for that admission.

Furthermore as the president's attorney he can't be compelled to testify against his own client.