Thank you all for your advice.
I've decided that I'm going to cut the tree down.
I'll probably wait until after the leaves fall.
Besides the problems you've mentioned, the tree also makes a mess.
I think it has antracnose. It suvived the initial attack several years
ago, but every year many leaves turn yellow and fall to the ground
especially in the spring, but continuing all summer long.
Also squirrels eat most of the nuts or knock them to the ground.
I've never had a walnut from the tree, even though it produces lots of
them.

Barry