UK Prime Minister Sir Keir Starmer wants a guarantee of U.S. military intervention in Ukraine in a worst-case scenario to ensure any future peace deal there goes ahead. Speaking in Paris after an emergency summit with European leaders on Monday, Starmer said U.S. backing is the “only way to effectively deter Russia from attacking Ukraine again.” And he said the future of Ukraine is not the only thing at stake. “It is an existential question for Europe as a whole, and therefore vital for Britain’s national interests,” he added. “This is a once in a generation moment for the collective...