Bush's most contentious move came in the form of a military order approving the use of the military tribunals to put accused terrorists on trial faster and in greater secrecy than a regular criminal court.

Obama also has wielded considerable power in secret, upsetting the more liberal wing of his own party. He has carried forward Bush's key anti-terrorism policies and expanded the use of unmanned drone strikes against terrorist targets in Pakistan and Yemen.

When a promised immigration overhaul failed in legislation, Obama went part way there simply by ordering that immigrants brought illegally to the United States as children be exempted from deportation and granted work permits if they apply. So, too, the ban on gays serving openly in the military was repealed before the election, followed now by the order lifting the ban on women serving in combat.

Those measures did not prove especially contentious. Indeed, the step on immigration is thought to have helped Obama in the election. It may be a different story as the administration moves more forcefully across a range of policy fronts that sat quiet in much of his first term.

William Howell, a political science professor at the University of Chicago and the author of "Power Without Persuasion: The Politics of Direct Presidential Action," isn't surprised to see commandments coming at a rapid clip.

"In an era of polarized parties and a fragmented Congress, the opportunities to legislate are few and far between," Howell said. "So presidents have powerful incentive to go it alone. And they do."

And the political opposition howls.

Sen. Marco Rubio, R-Fla., a possible contender for the Republican presidential nomination in 2016, said that on the gun-control front in particular, Obama is "abusing his power by imposing his policies via executive fiat instead of allowing them to be debated in Congress."

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