On November 21, the EU and Beijing both filed separate cases against the US with the World Trade Organization. In each case, they've posited that the justification Trump provided for his tariffs - US national security - is invalid. Their complaints were also echoed by Mexico, Norway, Canada, and Russia.

"If they can decide themselves anything is a national security interest...you don't have any rules anymore in the WTO," said the chief of staff to Trade Commissioner Cecilia Malmstrom, Maria Asenius. Experts believe the case is more about the principle of the matter than an attempt to pressure the US into backing off its tariff plans.

The complaint represents a setback for the US, which had hoped the EU and other countries would join its fight against Beijing.

The WTO challenge is a break with tradition. As a general rule of trade diplomacy, countries respect such justifications. Experts are concerned that this may upset the entire international trading system.

If the WTO rules in favor of the US, that could encourage other countries to use similar justifications to enact their own tariffs, even if seemingly groundless. If the WTO rules against the US, the US could quit the WTO altogether. Trump has previously criticized the WTO, calling it unfair and against American interests.

Trump is not the only one who has expressed dissatisfaction with the WTO. Indeed, at the recent G20 summit, global leaders agreed that the WTO is not achieving its objectives and issued a memo committing to reform. It's unclear when or how these reforms will manifest. The announcement was framed in such a way to appease the US, including none of the WTO's typical language committing to fight protectionism. It also removed phrasing related to "fair trade practices" that could offend China, which has denied allegations from the US, the EU, and other Asian countries that it engages in unfair tactics like using industrial subsidies and violating intellectual property rights.

It's unclear if the proposed reforms will in any way impact the outcome of the tariff case. After the G20 summit, Trump and Chinese President Xi Jinping reached a 90-day tariff truce while the results of trade negotiations are pending; it's unclear if the results of these negotiations might impact the WTO cases.

The WTO panels are expected to make their decision within nine months, though the appeals process could extend the issue much longer. There's a similar case involving Qatar and Russia which, though less geopolitically critical, may result in an earlier precedent.