Betting is now 37% Supreme Court upholding IEEPA tariffs.

Source: Kalshi, accessed 10/23/2025.

What happens if the IEEPA tariffs are struck down, effective tariff rate-wise?

Figure 1: Average effective tariff rate (blue), average declared tariff rate (tan), and average effective tariff rate if IEEPA tariffs are struck down (light blue), all in %. Calculations assumes October values of customs revenue and imports both the same as September. Assumes in October, $200 bn revenue (SAAR) comes from IEEPA tariffs per Tax Foundation. Source: OECD Interim Economic Outlook, Paweł Skrzypczyński, Tax Foundation, and author’s calculations.

I’ve used 1/10 of the Tax Foundation’s $2 trillion estimate to guess at the reduction of IEEPA tariff revenues. This is an approximation, with out-years likely having more tariff revenue due to trending imports, while more comes in early because pre-substitution timing; I’m assuming the effects offset each other.

Of course, Mr. Trump could then try to use Section 201 or other authority to impose tariffs (see here for list), although some of those alternatives would require time to implement.