While cautioning that Obama has made no final decisions, officials say there is a difference between last year's effort to strike Syria's government in retaliation for chemical weapons use and a bombing campaign against Islamic State militants that is now under consideration. The militants have been moving with ease between Iraq and Syria, effectively blurring the border between the neighboring nations. [...] far, there has been little clamor among congressional leaders for Obama to seek approval from Capitol Hill before proceeding with military action in Syria. Legal experts say Obama would have the authority to launch strikes in Syria without congressional approval, though they say his standing would be strengthened if the scope and duration of the attacks were limited. The White House offered a trio of justifications for the unilateral action: an imminent threat to American personnel stationed in Iraq, a request for assistance in countering the militants from the Iraqi government, and a humanitarian crisis in northern Iraq where militants had trapped religious minorities. Defense officials say the U.S.