When the OLC opined in 2000 that a president cannot be indicted, one reason was that a statute of limitations could be "equitably tolled" (i.e., stop the clock).
I just can't find any precedents for criminal equitable tolling...
That's a problem.
What if presidential immunity doesn't toll?
Prosecutors must indict.
Equitable tolling in civil cases usually turns on something the defendant did to hide or delay. But if a prosecutor declines to indict, then president has done nothing actively to lose his S of L claim.
Courts could say to future prosecutors, "You made all the assumptions and did nothing. We never said anything about immunity. Why should pres lose? You lose."
Perhaps prosecutors could issue a report: "But for pres immunity, we would have sought indictment."
But if so, then why not just indict?
The only sure way to deal with tolling:
Indict a sitting president.
then it does not inspire much confidence in the strength or seriousness of its legal conclusions. Does it?