Before you think presidential immunity, campaigning is not part of presidential duties. Those who attended Donald Trump rallies and were encouraged not to wear masks or have social distancing and required to sign waivers of liability, there is a valid argument that such waivers or void against public policy. If you attended and got the virus, sue.
Further, Donald Trump and the Republicans knew people would be flying in and flying out with the newly acquired virus is read to others. The victims did not sign waivers. if contact can be traced to a participant at one of the rallies, Sue. Likewise, all who voluntarily went to these rallies knew they would be endangering other people when they returned. Sue them as well..
It is time to use the courts to make people realize they owe a duty to others not to cause harm.
Sue. you will win.