Every president has used the power of executive clemency in the waning days of their presidency to pardon criminals who petition the Justice Department. Some have misused this power, pardoning undeserving felons or, in the case of Bill Clinton's pardon of financier and Democratic mega donor Marc Rich, added a political twist to clemency. 

It's unknown how many pardons President Obama will grant. But given the fact he has already pardoned 148 pardeons since taking office in 2009, it's a safe bet that dozens of criminals will be set free before his term is up. There are several high profile felons who may be on the list.

AFP:

Among them is Bowe Bergdahl, a US Army sergeant held captive for five years by the Taliban before his release in a prisoner swap, who is due to be court-martialed for desertion.

Leonard Peltier, a Native American activist convicted for the 1975 deaths of two FBI agents in what his supporters say was a setup, is also hoping to enjoy Obama's good graces.

Then there's Edward Snowden, who made the shattering revelation in 2013 of a global communications and internet surveillance system set up by the United States.

The 33-year-old, a refugee in Russia, is backed by numerous celebrities like actress Susan Sarandon and singer Peter Gabriel, as well as Amnesty International and the American Civil Liberties Union.

- Preventive clemency -

If Obama fails to pardon Snowden, his supporters say he may face the death penalty under the incoming administration of Republican Donald Trump, who has called him a "terrible traitor."

In another leak case, Chelsea Manning is serving a 35-year sentence in solitary confinement for handing 700,000 sensitive military and diplomatic documents to WikiLeaks, some of them classified.

Activists say her sentence is excessive and point to the psychological frailty of the transgender soldier who has already made two suicide attempts.

Even though the White House has dismissed a possible pardon for Snowden and Manning, their supporters are still hoping for a final magnanimous gesture from a president about to leave the constraints of his high office on January 20.

But both cases present unique challenges: Snowden has yet to be sentenced and merely faces espionage charges in the US, while Manning has an appeal pending before military court.

The US Constitution allows a president to pardon "offenses against the United States" and commute -- either shorten or end -- federal sentences.

Obama has so far granted 148 pardons since taking office in 2009 -- fewer than his predecessors, who also served two terms, George W. Bush (189) and Bill Clinton (396).

But he has surpassed any other president in the number of commutations, 1,176.

Another high profile petitioner is former Illinois Governor Rod Blagojevich who is looking to have his 14 year sentence for corruption reduced or eliminated. 

The president doesn't consider selling drugs a serious crime, so there are likely to be many drug dealers on his pardon list. As for those high profile cases mentioned above. I'm sure Obama would love to pardon Leonard Peltier, the native American activist who was involved in the shooting deaths of two FBI agents during unrest at the Pine Ridge Indian Reservation. Peltier's cause has been championed by everyone from the pope to left wing actors. No doubt Obama believes Peltier innocent as well.

Don't be surprised if Obama pardons and commutes the sentences of more felons than any president in history.