The most deadly witness in the Biden impeachment inquiry is due to testify Tuesday in a closed-door interview on Capitol Hill. He will be able to lay out in forensic detail the times he knows that Joe met with Hunter’s business partners, both during and after his vice presidency. He will bring documents in which the Chinese talked of their delight about doing business with the “B family” and the encrypted messages and emails in which Joe was referred to either directly or in code as “the big guy” or by Hunter as “my chairman.”