Here ya go VV.
Gall on native Sumac?
Maybe that's just the male plant...
Impressive galls, indeed. I'll bust out my Sinclair & Lyons (or the other fat text on Insects that Feed on Trees and Shrubs) and get you a positive ID.
Can't make out the stems - are those on Rhus glabra (Smooth Sumac)?
This may be a good source for what you've shown:
The galls of Pemphigus rhois Fitch (Fig. 113) are large, bladdery and evidently the pocketing of a single leaflet of the host plant, Rhus glabra or R. typhina. My specimens of these galls were fully mature, and I was therefore unable to follow the line of development. The leaf structure was modified into the characteristic Aphididae gall structure. Fibro-vascular bundles were numerous and near the inner surface of the gall. Opposite each bundle was a large cavity filled with some substance which I was unable to determine.
But this image looks spot on...
There are lots of hits on Melaphis rhois...
An exact match on the Melaphis rhois. Thanks. Like the links says, it's never really been an issue with the health of the host plants just an unsightly formation.