What consequences should Gary face?
Firstly, he would be involved on murder. That's not a great experience to have, for most people.
He would at least be on trial. I don't exactly know how incitement to murder is treated in the US.
It could even be considered domestic terrorism (an assassination made to intimidate a group based on an ideological agenda/government policy). Then, I don't know what would happen, exactly. The FBI would probably get involved?
https://missionlocal.org/2024/01/y-combinator-ceo-garry-tans...
This would not change ex post facto because of someone else's actions.
In the US, what he did said is disgusting but legally protected free speech. It's conceivable that he could be opened up to a civil lawsuit, but that's about it.