As the battle intensifies over how much authority President Barack Obama has to take executive measures in the face of congressional inaction, James Madison and Richard Nixon provide the frames of reference.
Madison, the architect of the U.S. Constitution in the late 18th century, envisioned recurring tension between the executive and legislative branches. Nixon, the first president driven from office by impeachment, demonstrated what abuse of executive power looks like.
The Republican-controlled House is planning to sue Obama for exceeding his executive authority, and threats of impeachment are in the air if, as expected, the president unilaterally exempts -- at least temporarily -- more undocumented immigrants from deportation.
This isn't a new fight.
"There always is tension with the executive when public policy can't be made in the legislative process," says Stephen Wayne, a professor of government at Georgetown University and a scholar of the presidency. "Since this often is partisan-based, it's more evident in times of divided government."
When John F. Kennedy won the presidency, most liberals argued for a strong executive, inspired by James MacGregor Burns' seminal book, "The Deadlock of Democracy."
When Nixon became president, liberal historian and Kennedy confidant Arthur Schlesinger wrote a book condemning what he called "the imperial presidency"; this was before any of the White House's illegal acts were revealed.
During the George W. Bush administration, there was no more jealous guardian of executive powers and privileges than Vice President Richard Cheney. As conservatives take on Obama today, Cheney largely is silent on this issue.
Much of the current legal wrangling goes back to a 1952 Supreme Court decision that found President Harry Truman didn't have the authority to seize U.S. steel mills.
In a concurring opinion, Justice Robert Jackson sought to enumerate the parameters of executive authority. Clearly, the president couldn't defy an act of Congress but could use executive authority to follow legislative measures.
In between, Jackson declared, there was a "zone" of concurrent legislative and executive powers that depended on the particular circumstances.
Nixon ultimately posed no problem because his acts violated the law. No president can order the Central Intelligence Agency to interfere with a domestic investigation or use the Internal Revenue Service to go after political enemies or order illegal break-ins. That's the easy stuff.
It gets harder mainly on national security matters. Did Bush overstep in approving wiretaps without warrants or the use of torture after the Sept. 11 attacks? Likewise, did Obama go too far with drone strikes or using force in Libya without going to Congress?
Courts generally prefer these questions to be settled by politicians. When the Democrats took control of the House in 2007, some liberals wanted to commence impeachment proceedings against Bush for his anti-terrorist actions.
The new speaker, Nancy Pelosi, categorically refused, which still rankles some left-wingers.
This summer, Obama is expected to decide whether to protect millions of undocumented immigrants from deportation. He took similar action two years ago for the so-called Dreamers, younger immigrants who came to the U.S. illegally but got an education and have otherwise abided the law.
Critics say that would amount to an unconscionable usurpation of executive authority, perhaps even laying the grounds for impeachment.
It may or may not be desirable policy or good politics. It wouldn't, however, defy a mandate from Congress, which has failed to do anything on immigration.
"The main effect of Obama's proposal would be to officially recognize current practice," Eric Posner, a law professor at the University of Chicago, wrote recently.
Even most immigration-reform opponents no longer advocate deporting 11 million undocumented immigrants.
For all the clamor, the legitimacy of executive actions -- whether by Bush or Obama -- will be settled in the political arena.