United States President Donald Trump held a 'Make America Great Again' rally in Columbia, South Carolina as he campaigned for a Republican candidate for state governor on Monday evening.

While Trump covered many topics at the rally, trade policies was a subject raised on several occasions as he received approving applause from supporters in the stands.

"The European Union doesn't allow our farmers to go in trade, it's very hard for them to go trade and if they do it's very expensive," he said. "That's essentially a trade barrier you can't trade, how can we trade. We can't pay that kind of a tax. So I want the barriers taken down, I want our farmers to be able to trade."

The recent imposition of import tariffs by the U.S., and counter-measures by other countries, are also starting to affect global production and supply chains. Some U.S. steel and aluminium tariffs went into effect in April and additional tariffs begin in July.