Tonight on the Last Word: The Washington Post reports that the Justice Department is investigating Donald Trump’s actions regarding January 6 and the effort to overturn the 2020 election. Also, Attorney General Merrick Garland won’t rule out prosecuting Trump. And the U.S. Secret Service faces criticism over missing texts. Carol Leonnig, Neal Katyal, Laurence Tribe, Andrew Weissmann and Jim Helminski join Lawrence O’Donnell.