US President Donald Trump, apparently impatient with the slow progress of negotiations, on Monday slapped 25 per cent unilateral tariffs on Japan and South Korea and equal or higher import taxes on several other nations ahead of a self-imposed Wednesday deadline.Analysts said the move shows that the mercurial American leader is using threats to jump-start negotiations.Trump sent two-page letters to Japanese Prime Minister Shigeru Ishiba and South Korean President Lee Jae-myung saying the new...