The United States will cut off Russia and “isolate” the country on the world stage, the U.S. ambassador to the United Nations vowed Sunday. “We can isolate them in the United Nations. We can isolate them in U.N. specialized agencies. They are feeling that isolation,” Ambassador Linda Thomas-Greenfield said ahead of an emergency meeting of the U.N. Security Council. Appearing on NBC’s “Meet the Press,” Thomas-Greenfield said the U.S. would push for a General Assembly meeting Monday and promised that Russia “will be called out and their aggressions will be brought to the attention of the world.”…