I know there have been discussions on this topic but I can't seem to
find a definitive answer.

I only hear 1 click when turning the ignition.  This especially happens
in the morning after not driving for the car for several hours.  After
turning the key several times, the car will start like normal.  Later
in the day, the car starts on the first try.  THEN, the other day, the
starter would not stop cranking after the car was started, even after
turning off the car.  The only solution was to pull the battery cables.

I took the car to the shop and everything started working fine (go
figure).  They even tested it first thing in the morning and the car
started fine.  They told me, without witnessing the problem firsthand,
that it's either a bad starter or starter relay.  Does anyone know
exactly what is causing this?  Starter, solenoid, starter relay,
ignition switch???

Thanks.