So What CAN'T a President Do by Executive Action?

Taxes, divorce law and seizing property are no-nos.

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."

The White House, Then What?

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."

Oct. 2, 2012 --

Tomorrow, the first of four debates among the presidential and vice presidential candidates will take place. President Barack Obama and Governor Mitt Romney will meet in Denver, Colo., on Oct. 3 for the first of three debates. Vice President Joe Biden and Rep. Paul Ryan will take the podium on Oct. 11 for their only joint appearance. Debates can define a campaign. Since 1960 when the first televised presidential debate was held between then-Sen. John F. Kennedy and Vice President Richard Nixon, candidates' performances at these events can alter the course of an election. In fact, a single line is enough to alter a candidate's fortunes. In this slide show, explore the one-liners that resonated the most in past presidential elections.

During the Cold War, there wasn't much question where the West ended and the Iron Curtain dropped -- unless you happened to be President Gerald Ford. At a 1976 presidential debate with then-Governor Jimmy Carter, Ford proclaimed: "There is no Soviet domination of Eastern Europe, and there never will be under a Ford administration." The remark stunned the moderator, Ford's opponent and the audience of the first televised debate since Kennedy met Nixon. Ford's already shaky campaign tanked, and Carter won the presidency handily.

Days ahead of the New Hampshire Republican primary in 1980, then-Gov. Ronald Reagan's campaign sponsored a debate in Nashua to reinvigorate his campaign. Although he was an early favorite to clinch the nomination, he had recently lost the Iowa caucuses to George H.W. Bush, who claimed to be gaining momentum. Before the debate began, there was a behind-the-scenes discussion of who would be included on stage. As this question was being discussed, the moderator, John Breen, instructed technical support support to cut off Reagan's microphone. "I am paying for this microphone, Mr. Green," Reagan replied, insisting that he be allowed to speak. Reagan's remark was well received by the audience and helped boost his primary campaign. The former president himself even credits the moment for playing a role in sending him to the White House.

SLIDE SHOW: Ronald Reagan at 100, in His Own Words

In the 1984 Democratic primary to face incumbent Ronald Reagan, former Vice President Walter Mondale and Sen. Gary Hart were locked in a tight race. Mondale was seen as more of the establishment candidate, while Hart represented a fresh face for the party. Beginning in a debate held in March 1984, Mondale pressed Hart whenever the senator raised the issue of "new ideas" he had with the phrase: "Where's the beef?" The slogan had been used previously by fast-food chain Wendy's within their commercials. Mondale's call for specifics and depth to Hart's policy proposals proved successful in attracting voters to his campaign, and he eventually clinched the nomination.

After four years in office, Reagan was up for reelection in 1984. At the time, he also happened to be the oldest president ever to serve in office. This led to speculation about his mental fitness for office. In his second debate with former Vice President Walter Mondale, Reagan remarked: "I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience."

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In an attempt to convince voters that he had the experience necessary to assume the office of the vice presidency, then-Senator Dan Quayle frequently framed his argument comparing himself to the late president Kennedy, claiming the two had the same number of years in Congress before seeking higher office. In a 1988 vice presidential debate with Democratic Sen. Lloyd Bentsen, Quayle again made the comparison, which Bentsen took issue with. "Senator, I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy," the elder senator remarked to a crowd roaring with laughter and applause. Quayle objected to the remark, calling it uncalled for in the debate.

"Who am I? Why am I here?" These are the words that Vice Admiral James Bond Stockdale, independent candidate Ross Perot's running mate, opened with at a vice presidential debate in 1992. With little forewarning and no preparation ahead of the debate, Stockdale appeared on the podium appearing confused and listless when compared to the considerably most polished Republican and Democratic candidates, Vice President Quayle and then-Sen. Al Gore.

During the 2008 campaign, Sen. John McCain frequently mentioned that he was not responsible for a single earmark during his tenure in office. At a Republican presidential primary debate in 2007, McCain noted his opposition to a $1 million federal earmark for a museum dedicated to Woodstock. "Now my friends, I wasn't there. I'm sure it was a cultural and pharmaceutical event. I was -- I was tied up at the time," McCain remarked. McCain managed to simultaneously remind the crowd of his service in Vietnam, his experience in the Senate and his sense of humor all in one breath.

In 2008, then-Senator Barack Obama rode a wave of popularity to claim victory in the Iowa caucuses, an outcome that shook up the race in his favor. Ahead of the New Hampshire primary, Obama appeared to be the favorite against then-Sen. Hillary Clinton. In a debate prior to the primary, the moderator asked Clinton how she could compete with Obama's likability. As Clinton started to give her answer, Obama interrupted with: "You're likeable enough, Hillary." The comment ended up playing in Clinton's favor as her supporters rallied around her, claiming both the media and her opponents were too quick to write her off. Her eventual victory in New Hampshire helped draw out what turned out to be an extended primary process.