It seems to me that the amount of income from Import Tariffs is vastly less than what would be potentially earned.
According to The CIA World Factbook, the US had approximately $2.361 trillion dollars worth of imports in 2017. With the current maximum, the tariff would only be about 0.23%. For the UK, there were about $615.9 billion in imports in 2017, making the tariff about 0.12%.
While the numbers have surely changed a bit since then, this is still pretty low. I highly doubt a tariff of less than 0.5% would reduce International Trade by 45%.
Also, the income of the tariff should probably be scaled by the amount of International Trade.