Understanding the Implications of Today's Terrorist Attack in Russia

Reports are coming out with ISIS taking credit for the attack in Moscow today. That is still potentially problematic for the United States, who has been linked in the past providing military assistance and training to Islamic extremists in Syria. The U.S. made a major blunder by immediately insisting that Ukraine did not carry out the attack. That suggests the U.S. knew who carried out this vicious act of terrorism and failed to warn Moscow.