Just get a projector and let him present via webcast. Not sure I'd want to risk coming to the US if the authorities might detain me for something I did as a teenager. (not saying this individual did that, but example.)

It's not the same thing. Better to move the conference to a country more conducive to international collab then.

Sorry he won't webcast. Americans can buy tickets and go to his country if they wish to be among smart peers.

> He's visiting a conference not immigrating.

Crazy thought: perhaps the visa folks are thinking that he already missed the conference and they have stacks of other work to do.