The mechanism: Every container that clears the Ports of Los Angeles and Long Beach and heads inland has to get off the dock somehow, and for the huge share bound anywhere east of the Rockies, that means a railcar. Union Pacific owns the western half of that bottleneck outright — it's the only Class I with direct rail access into LA/Long Beach, plus Oakland, Tacoma, and Seattle. That makes UNP's international intermodal carloads one of the cleanest leading indicators in the market for how much Chinese-origin freight is actually moving, weeks ahead of when it shows up as revenue on a Walmart or Target earnings call. Right now that indicator is unusually policy-sensitive: the November 1, 2025 Trump-Xi trade agreement pushed 178 active Section 301 product exclusions out to November 9, 2026, and USTR's own notice states the extension exists specifically so importers keep sourcing decisions stable through the deadline. Every renewal, expansion, or lapse of that exclusion list is a direct lever on how many containers get loaded onto UNP's western network — and the read-through hits the railroad's weekly AAR carload data before it hits anyone's income statement.