Glad I chose to replace this before adding an Anker 6 outlet surge protector… the bottom outlet must have shorted at some point and we could never get a plug in it since we bought the house #diy #electrical #grownostr 
Discussion
The screw wasn't tightened enough on the wire, or the wire was damaged, or changed shape over time (can happen if the wire is tinned with solder, or made of aluminum). This causes resistance and possible arcing when loaded, both producing heat.