My Sassafras patch is thriving after removing a few saplings that were blocking sunlight. I located another Sassafras near my driveway that would benefit from clearing more saplings and a few of the larches that the previous property owners planted (that are not doing well in that location anyway).
The Clustered Bellflower is a food source to butterflies and other pollinators so I will let it stay.
The book New England Wildflower Society’s flora Novae Angliae : a manual for the identification of native and naturalized higher vascular plants of New England by Arthur Haines (2011) indicates that Campanula glomerata has been found in many New England states except Connecticut. I’m guessing a migrating bird dropped the seeds and they are now naturalizing.