Future historians will ask why George W. Bush sought and received express congressional authorization for his wars (against al Qaeda and Iraq) and his successor did not. They will puzzle over how Barack Obama the prudent war-powers constitutionalist transformed into a matchless war-powers unilateralist. And they will wonder why he claimed to “welcome congressional support” for his new military initiative against the Islamic State but did not insist on it in order to ensure clear political and legal legitimacy for the tough battle that promised to consume his last two years in office and define his presidency. MoreIraqi Refugee: ISIS Wouldn’t Exist Under SaddamThe Islands Stuck in the Middle of Scotland’s Vote for IndependenceWatch Live: Oscar Pistorius Cleared of Murder, Verdict Continues NBC NewsA Nation Mourns: Remembering 9/11 on the 13th Anniversary NBC News'If You Threaten America, You Will Find No Safe Haven' NBC News“History has shown us time and again .