President Donald Trump's new tariff orders against Canada, Mexico and China all contain clauses suspending a duty-free exemption for low-value shipments below $800 that is widely seen as a loophole that has allowed shipments of fentanyl and its precursor chemicals into the United States.

But Mr Trump’s most incendiary claims are reserved for China. The Communist Party, he says, “has subsidised and otherwise incentivised” Chinese firms to “export fentanyl and related precursor chemicals that are used to produce synthetic opioids sold illicitly in the United States”.

President Donald Trump on Saturday signed an order to impose stiff tariffs on imports from Mexico, Canada and China, drawing swift retaliation and an undeniable sense of betrayal from the country’s North American neighbors as a trade war erupted among the longtime allies.