After months of threats, President Trump is abruptly re-escalating the trade war.For businesses craving certainty, who've had a period of relative calm, the move could once again upset that balance.It also injects a new risk into financial markets that have largely already moved on to a post-tariff world.

By Jeff Mason, Bart H. Meijer and David Brunnstrom WASHINGTON/BRUSSELS (Reuters) -U.S. President Donald Trump opened a new phase on Monday in the trade war he launched this year, telling partners, from powerhouse suppliers such as Japan and South Korea to minor players,