NATO, the strongest and most successful alliance the world has ever known, is celebrating 75 years of collective defense. Andrea Mitchell is joined by Clifton Truman Daniel, the grandson of President Harry Truman, who presided over the signing of the North Atlantic Treaty, and presidential historian Michael Beschloss to discuss the legacy of President Truman and NATO. » Subscribe to MSNBC: youtube.com/msnbc Download our new MSNBC app for the latest breaking news and daily headlines at a glance: msnbc.com/information/download-msnbc-app-n1241692 Follow MSNBC Show Blogs MaddowBlog: msnbc.com/maddowblog ReidOut Blog: msnbc.com/reidoutblog MSNBC delivers breaking news, in-depth analysis of politics headlines, as well as commentary and informed perspectives. Find video clips and segments from The Rachel Maddow Show, Morning Joe, The Beat with Ari Melber, Deadline: White House, The ReidOut, All In, Last Word, 11th Hour, and Alex Wagner who...