There ARE certain situations where the time for computing Statute of Limitations does not run. One of those situations, for example, is if the crime could not have been discovered due to the perpetrator's fraudulent behavior (i.e. a "cover-up"
. Do we have that situation here? I think an argument could be made on either side. I think one could argue that the "cover-up" was only DISCOVERED this weekend (when the Mueller Report was issued), and therefore the Statute of Limitations time should START then.
Another situation is if the perpetrator of the crime fails to show up for court or otherwise goes "on the lam." You can't avoid the court and just wait out the Statute of Limitations and then walk away from it. In this case, I suppose you could argue that Trump is avoiding service of summons as a result of his job, but that's kind of a weak argument.
All in all, I'd say that the best way to go about this is for whichever Court decides to prosecute Trump to just go ahead and file a criminal complaint against him just before the Statute of Limitations runs out, REGARDLESS of whether or not they think it will be honored. They will certainly have to argue that issue out, and if they win, they've preserved their right to prosecute him, even if the arguments take years. And it may preserve the issue long enough for Trump to be out of office, which would then make them moot.
Of course, the BEST course of action is just to boot his ass out in 2020 (or before) and not have to worry about the whole Statute of Limitations argument.