Mr Trump, in his tweet on 2nd December, blamed Brazil and Argentina for devaluation and argued that it is affecting the US farmers. Therefore, he restored the tariffs on all steel & aluminium imports to the US from both countries.
The decision is going to hurt the American steelmaking industry itself, which particularly needs steel slab currently exported by Brazil. In the past, Brazilian steel producers avoided the 25% US tariffs under section 232 by accepting a hard quota system proposed by the US Department of Commerce in May 2018.
Under the deal, Brazil was allowed to export up to 3.5 million tonnes of semi-finished steel (mainly expected to be slab) and around 600k tonnes of finished steel to the US.