I measured the resistance across each of the two thermostats and found that the thermal fuse was open (bad). The root cause of the problem was that the lint screen was not seating all the way down, which over time caused a large build up of lint in the dryer housing (before the fan) and throughout the duct work. This caused the dryer to over heat, and the thermal fuse correctly opened to avoid a fire. I disassembled the door to thoroughly clean out all the lint by hand and with a vacuum, and got the screen to seat properly again. I replace the duct outside the dryer and improved the airflow. Then I replaced both the thermal fuse and the hi-limit thermostat. All of this was simple and did not take long. I spend more time cleaning out the dryer than replacing the small parts. It is really important to understand why the thermal fuse tripped and to fix that.