Tonight on The Last Word: Pennsylvania leads the U.S. in political ad spending. Also, former national security leaders endorse Vice President Harris. Plus, Manhattan District Attorney Alvin Bragg urges Judge Juan Merchan to reject Donald Trump’s bid to toss his conviction. And gun safety group March for Our Lives makes a historic endorsement. Sen. Bob Casey, Amb. Susan Rice, Andrew Weissmann, and David Hogg join Lawrence O’Donnell.