After the attack on American diplomats in Benghazi last month, President Obama vowed to hunt down the killers and bring them to justice. There is a good chance that this means that they will be incinerated by missiles fired from drones. If so, the United States will have used drones to kill members of al-Qaida and affiliated groups in Afghanistan, Iraq, Pakistan, Somalia, Yemen, and Libya—six countries in just a few years. Mali may take its turn as the seventh. This startlingly fast spread of drone warfare signifies a revolution in foreign affairs. And, for good or for ill, in an unprecedented way it has transformed the U.S. presidency into the most powerful national office in at least half a century.
In the past, presidents faced two major obstacles when trying to use force abroad. The first was technological. The available options—troops, naval vessels, or air power—posed significant risks to American military personnel, cost a lot of money, proved effective only under limited conditions, or all of the above. Dead and maimed soldiers, hostages, the massive expense of a large-scale military operation, and backlash from civilian casualties can destroy a presidency, as Vietnam and Iraq showed.
The second obstacle was constitutional. The Constitution includes a clause that gives Congress the power to declare war. Presidents have been able to evade this clause for small wars—those involving only naval or air power, or a small number of troops for a limited period of time. They have mostly felt compelled to seek congressional authorization for

Read more: Drones attacks in Libya: An unprecedented expansion of presidential power. – Slate Magazine.