A raised-arm salute by Stephen K. Bannon that to many resembled a Nazi gesture incited an outcry on Friday not just from liberal critics of President Trump and his allies but also from a leader of the European right. It came a month after Elon Musk made a similar salute, and at a combustible moment when the administration of Mr. Trump, who has long been dogged by charges of encouraging far-right extremism, appears to be leaning more aggressively into far-right alliances around the world. Mr. Bannon, a former chief White House strategist and a longtime thought leader in Mr. Trump’s...