This administration has been reluctant to try terrorists in military courts. Instead, in 2010, it attempted to try 9/11 mastermind Khalid Shaikh Mohammed in the Manhattan federal courthouse, not Guantanamo. Faced with widespread opposition, the U.S. government quickly abandoned its plans. Mr. Tsarnaev, a naturalized U.S. citizen, and therefore entitled to all the rights of citizenship, will be tried in U.S. federal court. He should be tried by military tribunal.