Is it possible to have a popover within a portal that has a portal in the popover?
No. Portals within a portal are not allowed (even in popovers).
However, what you can sometimes do is have a popover outside of the portal that accomplishes the same thing. The button in the portal opens the popover (which is external to the popover).
The trick to accomplishing this is to put a regular button in the portal row that does two things:
a) sets a field used as a match field in a relationship on which the popover's portal is based using data from the portal row.
b) uses go to object to open the popover.
The popover button outside of the portal is kept permanently hidden via entering True or the number 1 as its Hide Object When condition.
Retrieving data ...