Supreme Court tariff ruling nears; JPM maps S&P 500 swings across four scenarios

A Supreme Court decision on key Trump tariffs is expected in the current opinion window (with Feb 20 highlighted), and JPMorgan’s trading desk outlines sharply different equity outcomes depending on whether tariffs are upheld, struck down, or swiftly replaced. With ~$124bn in customs duties through January, fiscal incentives may reinforce rapid “replacement” efforts if IEEPA tariffs are curtailed.Summary:Markets are braced for a U.S. Supreme Court ruling on key Trump-era tariffs as early as Friday 20 Feb, with additional opinion days Tue 24 Feb and Wed 25 Feb also flagged. JPMorgan’s trading desk scenario tree assigns 64% odds to “struck down + immediately replaced,” limiting net upside after an initial spike (desk estimate).JPM’s framework also assigns 26% to “tariffs upheld” (risk-off), 9% to “struck down after midterms,” and 1% to “struck down with no replacement.”The U.S. has taken in roughly $124bn in customs duties through January FY2026-to-date, highlighting the fiscal stakes. If the Court curbs the IEEPA pathway, the administration may pivot quickly to other authorities (e.g., Section 232/301/122), keeping effective tariff pressure higher than a simple “strike down” headline suggests.A long-awaited U.S. Supreme Court decision on the legality of President Donald Trump’s most sweeping tariffs could land as soon as this week, setting up potentially outsized cross-asset moves for equities, rates and the dollar. The Court has scheduled opinion days for Friday, 20 February, with additional opinion release dates Tuesday, 24 February and Wednesday, 25 February, a window that has kept markets on alert after weeks of “any day now” speculation. Against that backdrop, JPMorgan’s trading desk has circulated a probability-weighted playbook for how equities might react. The desk’s distribution is best read as scenario framing rather than a forecast.JPM trading-desk scenario tree (desk estimates)64%: Tariffs struck down and immediately replaced → S&P 500 +0.1% to +0.2% after an initial +0.75% to +1.0% spike26%: Tariffs upheld → S&P 500 -0.3% to -0.5%, with larger yield-curve moves9%: Tariffs struck down after midterms → S&P 500 +1.25% to +1.5%, Russell 2000 outperforms1%: Tariffs struck down with no replacement → S&P 500 +1.5% to +2.0%, Russell 2000 outperformsThe intuition is straightforward: the more the ruling reduces the expected effective tariff rate and the longer that reduction lasts, the more supportive it is for risk assets, especially domestically oriented small caps. Conversely, an “upheld” outcome risks a near-term hit to sentiment and a sharper repricing in rates as markets reassess inflation, growth and policy constraints.Why the “replace immediately” case mattersA central market argument is that even if the Supreme Court strikes down tariffs imposed under the International Emergency Economic Powers Act (IEEPA), the administration may be able to reconstitute similar levies under different legal authorities (though with different process, scope, and timelines). Coverage ahead of the decision has repeatedly flagged potential alternatives such as Section 232 (national security), Section 301 (unfair trade practices), and other tools like Section 122, which could be used to restore tariff pressure quickly and cap the equity upside from a headline “strike down.” That “headline vs. effective rate” distinction is why the desk’s base case is not the most bullish branch. It also fits the broader market narrative: tariff regimes can shift how trade happens more than they shrink deficits outright, and the policy/legal endgame may be messy, involving partial findings, multiple opinions, and follow-on actions by the White House and Congress.The fiscal angle adds pressureTariffs are no longer a side-show line item. U.S. government data show customs duties totaling about $124bn through January (fiscal year to date), underscoring why a court-driven disruption could have budget implications—and why policymakers may be incentivised to find replacement mechanisms if a major tariff channel is constrained.What to watch on the tapeIn practice, the first market move may come from positioning and headline interpretation: whether the ruling is read as (1) a clean removal, (2) a partial trimming, or (3) a legal procedural limitation that still leaves wide latitude. The second move is likely to be about “replacement speed”—how quickly the administration signals alternative tariff plans and under which authority. That’s where the JPM desk’s “spike then fade” logic in the 64% branch comes from.
This article was written by Eamonn Sheridan at investinglive.com.

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