The official said Trump may operate under a different standard.
“We will reinforce old alliances and form new ones and unite the civilized world against radical Islamic terrorism, which we will eradicate completely from the face of the Earth,” Trump said minutes after taking the oath of office on Friday.
As ABC News has reported, al-Baghdadi has been assessed by senior military intelligence analysts for the past few months of being hunkered down in Iraq's second-largest city, Mosul, occupied by ISIS since June 2014 and the scene of his only appearance ever on video, delivering a sermon that summer from a mosque's pulpit against the West and proclaiming himself caliph, the leader of all Muslims.
Killing the No. 1 "high-value target" on the U.S. kill list has been a top priority for Obama but accomplishing that in a densely-populated city of an estimated 1 million or more civilians was a challenge that seems to have eluded the outgoing president.
Trump may be less hesitant than Obama to launch a strike in Mosul if intelligence operatives pinpoint al-Baghdadi's lair, in the view of many hopeful counterterrorism officials, who say they are eager to exterminate a terrorist who oversaw the butchering of tens of thousands including American and western hostages beheaded on video.
Still, a currently serving career intelligence official suggested Trump may be constrained by long-held legal restrictions on armed conflict, which limit foreseeable civilian deaths.
"Lawyers are lawyers," the official said.
"Trump is probably more likely to make decisions quicker when it comes to military actions, whereas the Obama NSC has been much more deliberative," said Hughes, now the deputy director of the Program on Extremism.
In a number of major special operations aimed at killing top leaders of terrorist groups or raids to free American hostages of terrorists, some career officials have said Obama's team waited too long and missed opportunities.
The White House has consistently denied such charges.
Top intelligence officials have said privately that al-Zawahiri is believed to have received help from current or retired Pakistani military intelligence officers.
Al-Zawahiri has issued dozens of video and audio speeches since then, including as recently as this week.