Beijing has vowed to retaliate against Washington’s expanded Iran sanctions targeting Chinese entities, threatening a clash that could erode recent stability in the US-China relationship and become a new flashpoint weeks before President Xi Jinping visits the US, according to observers.But they say that efforts on both sides, such as this week’s Track 1.5 dialogue, could serve as a check on tensions and allow each side to understand the other’s concerns.The US on Monday announced fresh...