France has cut off Charles Kushner, the U.S. ambassador and the father of President Trump's son-in-law, from meeting government officials after he failed to appear when summoned.Why it matters: America's diplomatic corps is supposed to manage its relationships abroad. But the Trump administration's ambassadors have repeatedly butted heads with foreign leaders, threatening to strain relationships with allies.Driving the news: Kushner was summoned after the State Department attributed the beating...