VESTMANNAEYJAR, ICELAND — Prime Minister Justin Trudeau joined the leaders of Nordic countries on Monday in expressing concern over the potential effects of this weekend's short-lived uprising in Russia, while stressing that their support for Ukraine remains steadfast. "We had obviously very serious conversations about possible implications of the internal challenges that Russia is facing," Trudeau said at a joint news conference with Nordic prime ministers in Vestmannaeyjar, Iceland, where he was a special guest at their annual meeting. "It is their internal challenges," he said. "But our strength in continuing to stand for Ukraine … to defend the values…