When people’s lives are wrecked it is easy for them to turn toward a demagogue promises them that things will be better, and just trust him, ok?
All things being equal, when economic status is comfortable the tribalism inherent in humans doesn’t have as much sway. When it isn’t, then passions really boil.
Unions still have influence over their members, which is why they are beginning to enter the fight against said demagogue. Even if trade deals are bad- and by and large they have been- electing someone who would be terrible for the country would also be bad for these workers.
The natural union constituency is one of the major bases for the demagogue, which makes their animosity toward him important, and the strength and efficacy of that animosity vital.
Therefore, unions are good and should not be destroyed. Strong private unions are good, and the attack on public sector unions, the last true protector of the working class, are bad.