Trade accounted for only 4% of GDP in 1930 so any trade bill could only have a marginal impact.
It would not be possible to assess the impact on “percentage of GDP” alone but in the importance to the overall activity of the economy.
We might not be spending all that much of our GDP on imported oil but make that stop by fiat edict and see what happens. Too much of the rest of the economy has leaned upon this convenience to expect anything but a major dislocation.
I would aver that a wiser policy is “balanced trade.” If the US exports enough widgets to Slobbovia to pay for the gimcracks it imports from Slobbovia, a zero tariff deal makes sense. Higher rates can be used as the stick, but balanced should be the carrot.
The problem with us is that we do NOT have balanced trade. We’re putting cheap junk on the national credit card which is already in a ridiculous state.