Today on "Meet the Press” former Rep. Beto O'Rourke (D-TX) talked about his mandatory AR-15 buyback proposal and his indifference to Joe Biden's age, Sen. Cory Booker (D-NJ) discussed the debates, health care and passing gun legislation in the Senate, and Rep. Liz Cheney (R-WY) thinks the world is safer under President Trump and wants to isolate Iran. Former Missouri Sen. Claire McCaskill, former Gov. of North Carolina Pat McCrory, NBC's White House Chief Correspondent Hallie Jackson, and Pentagon Correspondent for The New York Times Helene Cooper join the panel.Sept. 15, 2019