NEW YORK - City leaders across the U.S. are vowing to intensify their fight against President Donald Trump's promised crackdown on cities that protect people in the U.S. illegally from being deported.

New York City Council Speaker Melissa Mark-Viverito says, "We are going to become this administration's worst nightmare."

She was at a Monday gathering of municipal officials from urban centers such as San Francisco, Seattle, Denver, Chicago and Philadelphia.