WASHINGTON/BRUSSELS/SHANGHAI — The United States opened the way for more exemptions from its steel and aluminum tariffs on Friday, after pressure from allies and intense lobbying from lawmakers, further diluting the measures just a day after they were formally announced.President Donald Trump, who has broad powers to impose the tariffs of 25 percent on steel imports and 10 percent on aluminum, at the outset granted exemptions to Canada and Mexico, and said there would be the possibility of industry exemptions, although he has not been specific.After Trump opened the door, Brazil, Japan, South Korea, Australia and Europe clamored for special treatment, while Chinese producers called on Beijing to retaliate in kind.Trump tweeted on Friday that he spoke with Australian Prime Minister Malcolm Turnbull about trade and military cooperation.