From a reader:

I have a different take on the idea of “jobs Americans won’t do”. When
the Braceros program was being debated in California the tomato
industry claimed that ending the guest worker program would harm the
industry which was very dependent on low-cost labor to pick tomatoes
for ketchup. This is much sited by opponents of guest worker programs
since the ketchup industry responded by developing a different variety
of tomato that could be harvested mechanically and did just fine.
But if you look at the statement that picking tomatoes for ketchup was
a job that Amercans wouldn’t do you will find that, while it may suck
as an attitude, it was spot-on as a prediction. Americans never did
that job; the Braceros were replaced by machines.