We cannot see specific insect or disease signs. The problem is probably environmental. Many trees are dead or are still slowly dying in Maryland from the abnormal amounts of rain last year. Most plants cannot tolerate sitting it standing water or sodden/saturated soils, because the water replaces the oxygen in the soil and basically drowns the plants or weakens them and they get root rots. Evergreens, in particular, can manage to get through winter and cool spring all right, even when they are dying, but when summer comes with higher temperatures and pressure to grow, they can't. That's when they'll start to visibly decline.
If you know this site stays wet for long periods, you can try to improve the drainage there and, if the tree has enough healthy root system, it may recover.
If anything else in the vicinity has changed--such as the soil level was raised--that would also be an explanation.