Tonight on The Last Word: Donald Trump backs down from his latest tariff threat on Canadian metal. Also, Elon Musk won’t say Social Security won’t be interrupted. Plus, Ukraine agrees to the United States’ proposal of a 30-day ceasefire. And The New York Times reports tuberculosis is resurgent as Trump’s USAID cuts disrupt treatment globally. Catherine Rampell, Sen. Sheldon Whitehouse, and Dr. Atul Gawande join Lawrence O’Donnell.