My theory: Joe is on the laptop in pictures with his granddaughter. Hunter was molested as a kid. Hunter's kid. If you knew what was happening to your kid but knew you couldn't do anything about it, how would you lash out? Drug abuse? Debauchery? Nothing he did let him escape.
His whole fucked up life is because of that. He wanted out. Laptop drop was his way out. When Joe announced he was running for president, Hunter was done. He knew then they wouldn't allow him out of the family business.
When Trump asked "where's Hunter?" Trump already knew that he was with Trump's team in some way.
Godfather III