The European Union is threatening to target some of America’s most iconic brands if Donald Trump follows through on his threat to impose swingeing tariffs on imports of steel and aluminium.

Levi's jeans, Harley-Davidson motorbikes and bourbon could all receive tit-for-tat duty hikes, according to Jean-Claude Juncker, the European Commission president.

They include products manufactured in key Republican states as well as orange juice from Florida, a critical swing state in elections.

For his part, Donald Trump shows no signs of backing down, relishing the fight at a time when his White House is once again in crisis, roiled by resignations and awash with rumours of infighting.

"When a country (USA) is losing many billions of dollars on trade with virtually every country it does business with, trade wars are good, and easy to win," he tweeted on Friday morning. "Example, when we are down $100 billion with a certain country and they get cute, don't trade anymore — we win big. It's easy!"