Looks plain enough to me:"little, if any thing, was gained by the protection which the United States maintained in the first part of this [the nineteenth] century."
You simply don't like that conclusion so you try to obfuscate it with quote mining and out of context qualifiers.
It is easy enough to say "Tariff protection did not work." Taussig does not say that at all that is the reality of his study. He can't prove that it worked but neither can he prove that it did NOT work.