This market resolves based on the effective tariff rate for the United States in Q4 2025, defined as 100*(Customs duties)/(Imports of goods). I will resolve as per this FRED dataset by the St Louis Fed: 

https://fred.stlouisfed.org/graph/?g=1wn5e

The tariff rate for Q4 2024 was 2.63%. At the time of creation of this question, the highest rate since the start of this dataset was in Q4 of 1971, at 8.67%.

A report by the Yale Budget Lab suggests that the tax rate upon implementing all announcements by the Trump Administration up to and including the Liberation Day Tariffs will raise the tariff rate to 22.5% pre-substitution. 

https://budgetlab.yale.edu/research/where-we-stand-fiscal-economic-and-distributional-effects-all-us-tariffs-enacted-2025-through-april

[Notes: I will resolve upon the first publication of a datapoint for Q4 2025. If FRED updates the dataset, I will update the resolution. If this dataset stops being published, I'll find an equivalent.]