Forrest Pansy Redbud decline
These redbuds were planted at the same time and both had a late frost killing off new foliage. The one on the right has always not been as full red and has always had shoots coming up at the base of the trunk. This spring the leaves were always small and then just started dying is this a fungus and will it spread to the other tree? I can find no damage to the trunk or leaves.
Christian County Kentucky
I don't believe this is a disease. With such close proximity you would likely see disease on both. If it has always struggled then its possible the problem could be with the root system. Trees that are planted too deep or settle too deep into the planting hole will start to die as roots receive insufficient oxygen. I would also look for damage just under the soil surface caused by something chewing on the bark (voles are a possibility). Hard to say for certain from the photo but it's unlikely this tree will recover.