One possible reason for the decline of drone strikes in Pakistan is that the CIA is simply running out of targets; at least 36 militant leaders have been reported killed by drones in Pakistan since Obama took office, according to the New America Foundation data.

The growing criticism of the drone program in Pakistan has also surely had some role in the Obama administration's decision to scale back the intensity of the drone campaign there. In April the Pakistani Parliament formally voted for the first time to end any kind of approval for the CIA drone program.

Unlike in Pakistan where political leaders have almost universally -- at least in public -- condemned the strikes, Yemeni President Abed Rabbo Mansour Hadi said in September during a speech at the United Nations that he personally signs off on all U.S. drone strikes in Yemen, and that they hit their targets accurately, asserting, "The drone technologically is more advanced than the human brain."

The steadily increasing rate of drone strikes in Yemen over the past two years shows that the CIA's drone war -- rather than declining -- is shifting from one part of the world to another.

Brennan has been the key architect of this policy. The Arabic-speaking Brennan, who was once CIA station chief in Saudi Arabia, in a sense became the "case officer" for the Yemen "account," traveling to Yemen seven times since al Qaeda in the Arabian Peninsula sent the so-called underwear bomber to try and bring down Northwest Flight 235 over Detroit on Christmas Day 2009.

How effective has the subsequent U.S. campaign against this group been? Al Qaeda in the Arabian Peninsula has not tried to launch an attack on a target in the West since its abortive attempt to bring down cargo planes bound for the United States more than two years ago, so the campaign does appear to have suppressed the group's abilities to attack overseas.

According to a count by New America, at least 28 of the group's leading members have been killed in drone strikes, including the notorious American-born cleric Anwar al-Awlaki, who played an operational role in al Qaeda in the Arabian Peninsula, for instance, offering instruction to the underwear bomber.

Balanced, against this is the fact that some of the popular resentment against the U.S, drone campaign that has long been the case in Pakistan is beginning to emerge in Yemen. On Friday, dozens of armed tribesmen took to the streets of Rada'a protesting the drone strike that had taken place a day earlier. One of the tribesman told Reuters that seven civilians had been killed in that drone strike.

And the drone program in Yemen is also stirring some of the same controversy internationally that the strikes in Pakistan have done for many years. Human rights groups in the United States are particularly aggrieved by the targeted killing of al-Awlaki, an American citizen who was killed by a drone along with his teenage son.

Gregory Johnsen, who has written an authoritative book about al Qaeda in the Arabian Peninsula, "The Last Refuge: Yemen, al-Qaeda, and America's War in Arabia," says the group has grown from around 200 fighters to more than 1,000 and that the drone campaign has helped it to recruit these new fighters.