Long-term unemployment is a real phenomenon, and there is no debate in this country, at least practically speaking, that government welfare will be available to assist those who have fallen on hard times. It will be offered. The only question is how. Most of us consider that a morally good thing.
That means there may be another argument in favor of certain tariffs. If some tariffs can serve as a form of welfare, replacing transfer payments with jobs, and thus avoiding many of the dependency-related problems that accompany direct aid, they may prove to be a healthy policy solution in an imperfect world.
The possibility of putting a significant portion of our unemployed back to work and allowing them the dignity of self-support (with a small boost from government policy) is a political good that must be seriously weighed against the benefits of a freer trade environment.
If the question is what kind of welfare is going to be offered, might this not be the best kind? (On the flip side, of course, it must also be taken into consideration that this will typically harm workers in other countries who are even worse off than those protected in the United States.)