Russian President Vladimir Putin has put his nuclear deterrent forces on "high alert" as international tensions rise over Russia's four-day invasion of Ukraine. » Subscribe to MSNBC: http://on.msnbc.com/SubscribeTomsnbc 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, Meet the Press Daily, The Beat with Ari Melber, Deadline: White House with Nicolle Wallace, The ReidOut, All In, Last Word, 11th Hour, and more. Connect with MSNBC Online Visit msnbc.com: http://on.msnbc.com/Readmsnbc Subscribe to MSNBC Newsletter: http://http://MSNBC.com/NewslettersYouTube Find MSNBC on Facebook: http://on.msnbc.com/Likemsnbc Follow MSNBC on Twitter: http://on.msnbc.com/Followmsnbc Follow MSNBC on Instagram: http://on.msnbc.com/Instamsnbc #MSNBC #Putin #Ukraine