The judgment day for most of Donald Trump’s tariffs looms this week, with the US Supreme Court set to hear an appeal against a lower court’s ruling that they are illegal.

Should the Supreme Court rule against his administration’s reciprocal and baseline tariffs, the “Liberation Day” import levies of between 10 per cent and 50 per cent against all the countries the US trades with – and perhaps the trade and investment deals that have been struck using them as leverage – would have to be withdrawn, and the $US90 billion ($137 billion) or so in revenue the tariffs have generated so far might have to get refunded.

Donald Trump said the Supreme Court hearing is “one of the most important cases in the history of our country”.Credit: Getty

Trump could still have his tariffs, but he’d have to use different legislation that would involve extensive and time-consuming investigations, and couldn’t be imposed at the presidential whim. Or he’d have to resort to another law that puts a 15 per cent ceiling on tariffs, can only be used against countries with substantial trade surpluses with the US and sets a 150-day limit on the tariffs’ duration.

Trump used Section 232 of the Trade Expansion Act of 1962 – which required Commerce Department investigations – for his sectoral tariffs on steel, aluminium and cars, among other products. Those tariffs haven’t been challenged.

He said last weekend that the Supreme Court hearing is “one of the most important cases in the history of our country” and gave a dire warning of the repercussions if the tariffs were struck down by the court.

‘If a president was not able to quickly and nimbly use the power of Tariffs, we would be defenseless, leading even to........

© The Age