Both political parties are arguing whether President Barack Obama has the authority to grant legal status to millions of undocumented immigrants, but what are some of the actions that the president clearly cannot do? What are the defined limits to his power?
Many scholars say that presidential power has increased over the decades since President Harry Truman nationalized the U.S. steel industry during the Korean War. The Supreme Court struck down Truman's action, saying that it wasn't constitutional because it deprived the mill owners of their property.
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In times of emergency, the president can override Congress and issue executive orders with almost limitless power, according to Cornell University's Legal Information Institute. Abraham Lincoln used an executive order in order to fight the Civil War; Woodrow Wilson issued one in order to arm the United States just before it entered World War I; and Franklin Roosevelt approved Japanese internment camps during World War II with an executive order.
Many other executive orders are on file and could be enacted at any time, including more recent controversial orders about detention of terrorists, as well as collection of information by executive branch spy agencies on American citizens.
Michael McConnell, law professor and director of the Stanford Constitutional Law Center, said that presidents face a lot more restrictions on their powers on U.S. soil compared to what they can do overseas.
The conflict over executive power and the powers of Congress usually appear in two types of cases, McConnell said. "Trouble arises when the president acts when he has not been given the power to act," he said. "Or when he acts contrary to limitations that have been placed on him."
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Congress has forbidden various unilateral acts, such as overthrowing foreign leaders. But that power wasn't spelled out by the nation's Founding Fathers.
Georgetown Law School's Paul Rothstein puts it another way.
"There are a couple of things that are vague," Rothstein said. "Executive power is undefined in certain areas, and there is also the power to "do what is necessary" to carry out the laws of Congress. That's where there is some fudge factor."