The pardon only works for federal crimes.
So the options are state crimes, international crimes (against humanity), or somehow getting them classified as treason so they can use military tribunals. Or getting them on new crimes.
Lots of options.
I imagine it will be a mix.
At the end of this we might need a new constitutional amendment to limit presidential pardons.
Re midterms
I suspect Trump needs to be careful about exposing Dem crimes that he doesn't inadvertently energize their voter base.
It needs to be something that angers the middle enough to vote GOP without appearing too partisan that it encourages new throngs of idiot peach - mint voters.
Registry expires end of this month.
I don't think that secret pardons or a president pardoning himself have ever actually been tested by the courts… and presumably it would have to go to the Supreme Court.
Another reason to make sure conservatives have the majority?
But in any case it would be a protracted court battle, and secret pardons while dubious would probably be upheld.
So I'm guessing Trump had to find another way to get everyone.