Here is what presumptive immunity means [View all]

[MLAA]

What does presumptive mean in law?
Presumption is a legal inference that must be made in light of certain facts. For example, in the case of In Interest of Keiss, the Appellate Court of Illinois, Third District defined presumption as a legal inference; a party challenging it can overcome the presumption by providing the appropriate burden of proof.


So sure sounds to me a president is presumed to have immunity on actions while president, however they can be challenged in court. So appears challenges would then be decided by a judge or jury.