Diagnosis
The heating element has failed. This is a common failure. Without heat, the final dry phase cannot evaporate moisture. The element is located at the bottom of the tub under a cover.
How to Fix It
Replace the heating element. Part number is WD21X10094. Disconnect power and water. Remove the lower dish rack and the element cover. Disconnect the two wires, remove the mounting nuts, and lift out the old element. Install the new one, reconnect wires, and replace the cover.
If That Didn't Work
The problem could be the high-limit thermostat or the control board not sending power to the element. Use a multimeter to check for 120VAC at the element terminals during the dry phase.
Heads Up
The heating element gets extremely hot. Ensure the dishwasher has completed its cycle and cooled for several hours before attempting repair. Check for continuity of the new element before installing.