"Where they won't act, I will," he said in October 2011 as part of a "We Can't Wait" campaign he launched 10 months after Republicans took over the U.S. House of Representatives.

Since then, the president has turned to executive orders, policy directives, waivers, signing statements and other administrative steps to bypass Congress and act on contentious issues, including immigration, welfare, education reform and now gun violence.

Acting in response to the shooting rampage in Newtown, Connecticut, Obama announced 23 executive actions Wednesday designed to ensure guns don't get into the wrong hands. He also called on Congress to ban the sale of assault rifles, limit the size of ammunition clips and require background checks for all gun sales.

"Increasingly, what we're seeing is a lot of the policy-making apparatus of the federal government shifting to the executive branch," said William Howell, a University of Chicago expert on presidential powers.

Gun rights groups have accused Obama of an unconstitutional power grab.

"It's definitely not appropriate for the president to act unilaterally," said Erich Pratt, director of communications for the Gun Owners of America.

OBAMA'S ACTIONS ON GUN CONTROL 'SURGICAL'

Compared with some of the stronger steps Obama has taken in the past two years, his administrative actions announced Wednesday seem surgical. Most of what he proposed will have to be approved by Congress. He issued no executive order, which is the most formal tool a president has for pronouncing policy.

Obama did issue a presidential memorandum effectively overturning a congressional ban on federal research into the cause of gun violence.

He also acted administratively to get health care providers, states and federal agencies to share more information with the National Instant Criminal Background Check System, or NICS. This is an effort to prevent gun sales to people with disqualifying criminal backgrounds or mental health issues.

"These are all critically important," said Ladd Everitt, director of communications for the Coalition to Stop Gun Violence.

Even before Obama announced his unilateral steps on gun violence, critics began accusing him of overreaching his presidential powers. However, political analysts note that presidents since George Washington have used the same tools, especially when Congress is divided, as it is today.

Obama is not relying on executive orders themselves any more than other recent presidents. His 147 orders through four years is roughly the same pace as former President George W. Bush, who issued 294 in two full terms and Bill Clinton, who issued 308 in two terms.

CONGRESS SLOWED BY GRIDLOCK

Neither Clinton nor Bush faced a Congress as unproductive as the last one. It failed to pass a budget or a single one of 13 appropriations bills that fund federal agencies. It also has failed to pass a farm bill or overhaul the bankrupt Postal Service.

Only a few of the 147 orders Obama has issued have been controversial. Many are relatively modest, such as establishing advisory groups and task forces. Some have more substance, such as ratcheting up sanctions against Iran. And others are politically popular, such as one to identify and reduce regulatory burdens.

Obama used his third executive order, issued two days after his inauguration, to reverse earlier presidential signing statements by then-President George W. Bush that allowed harsh interrogation tactics.

Obama has bypassed Congress on at least four major issues:

-- In June 2012 he issued what became known as "the mini-Dream Act order." He directed the Department of Homeland Security not to deport undocumented immigrants brought here as children who meet certain other requirements. This came after a Senate filibuster two years ago killed legislation allowing immigration rights for people brought to the United States illegally as children.

-- In July 2012 he issued an "information memorandum" providing for conditional waivers from the workfare requirements of the 1996 welfare reform law in a way designed to give the states greater flexibility in how they reach the law's goals.

-- Starting in February 2012, Obama's Department of Education began issuing waivers giving states greater flexibility in meeting the requirements of the No Child Left Behind law enacted in 2001 as a means to make schools more accountable. Congress had been expected to incorporate many of the changes in a renewal of the act that was due in 2007. But it has failed to act over the past five years.

-- In October 2011, Obama instructed the Justice Department to no longer enforce the 1996 Defense of Marriage Act, saying it was unconstitutional. In a response that typifies Republican reaction to Obama's unilateral moves, former Republican Attorneys General Edwin Meese and John Ashcroft called the move "an extreme and unprecedented deviation from the historical norm."

Obama's "mini-Dream Act" order was perhaps his most aggressive. He effectively did for hundreds of thousands of people what Congress had specifically rejected since 2001, putting off the deportation of some who were brought to the country illegally as children by their parents.

"The Dream Act order is a decision by a president to implement a policy when Congress wouldn't give him the statute," said Kenneth Mayer, a University of Wisconsin professor of political science.

Analysts say the partisan gridlock of the moment is part of a longer trend in which the legislative branch, established under the Constitution as the first branch of the federal government, is giving way increasingly to a presidency.

"Congress has been taking themselves out of the game for several decades now," said Elaine Kamarck, who worked in the White House during the 1990s for then-Vice President Al Gore and now is a public policy lecturer at Harvard University's John F. Kennedy School of Government.

Obama formalized his intent to act more unilaterally in October 2009, 10 months after Republicans took control of the House.

Rarely does Congress or the Supreme Court reverse executive orders, according to legal scholars. When they are reversed or modified, it usually is by a future president. A rare example came in 1952 when the Supreme Court, ruling in the Youngstown Sheet & Tube Co. v. Sawyer case, rejected then-President Harry Truman's use of an executive order to put the steel industry under government control.