Police officers swarmed a cluster of anti-Trump protesters near the United Nations building in Manhattan on Tuesday morning, ahead of the president’s speech to diplomats and world leaders at the General Assembly. Dozens of demonstrators were milling in the streets near the U.N. roughly an hour before President Trump’s speech. More anti-Trump demonstrators were arrested nearby, according to the advocacy group Rise and Resist, which formed after Mr. Trump’s election to his first term in 2016. Alexis Danzig, a Rise and Resist member, stood in a line with other arrested protesters as they waited to be loaded into a police van. Ms. Danzig, her hands tied behind her back, said she had traveled from her home in Saugerties, N.Y., to protest Mr. Trump’s speech.