The timing will be tight. The Tulsa rally is on June 20th and the convention starts August 24th. It takes people about a month to die from Covid-19 and it may have an incubation period before any symptoms of 5-10 days. People who do get serious cases may be contagious during that 4-10 day pre-symptom period and not know it. So if everybody who went to the rally self-isolated for 14 days, then there would be little spread. But of course they won't.

I guess the real question is how many cycles of incubation and spread can they get in before the convention. If they go to group meetings, church, GOP insider get-togethers, etc. Then they could get the convention attendee infected population high enough for a truly massive superspread event.