You're being slothful again.
"little, if any thing, was gained by the protection which the United States maintained in the first part of this [the nineteenth] century"
In short, no gain. That means protection failed.
"Little" doesn't NOT mean no gain. "If any" is NOT a firm statement that there was none either. There is little, if any, chance I will be shot and killed on the street but to you this means I definitely will NOT be.
Just because you want it to mean what you want it to mean doesn't mean that it means what you mean.
It would have been simpler and easier for Taussig to boldly state "There was no gain from protection." But he was intellectually honest and knew he could not truthfully state that so he didn't leaving it to the intellectually dishonest to make that claim.
He states that the industries expanded prior to the tariffs due to the effects of war and embargo which were protectionist in the highest degree. Thus, the effect of the tariffs was more maintenance than infant industry protection.