Could Obama really be impeached over gun proposals?

President Obama had not yet officially unveiled any proposals on gun control, but Rep. Steve Stockman, R-Tex., had heard enough. He saw where this was headed.

"The White House's recent announcement they will use executive orders and executive actions to infringe on our constitutionally-protected right to keep and bear arms is an unconstitutional and unconscionable attack on the very founding principles of this Republic," he said in a written statement last week, two days before Mr. Obama presented his agenda to reduce gun violence. "I will seek to thwart this action by any means necessary, including but not limited to...filing articles of impeachment."

Stockman was quickly seconded by fellow freshman Rep. Trey Radel, R-Fla., who insisted that "all options should be on the table" in responding to the president's proposals, including impeachment.

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And judging from the outpouring that occurred on Twitter during and after the president's announcement, thousands of would-be constitutional scholars agree with the two freshman Republicans.

"OBAMA IS A CRIMINAL. WE HAVE A CONSTITUTION AND HE IS BOUND TO IT! NO MORE EXECUTIVE FIAT RULE! IMPEACH OBAMA!" read one of the more temperate tweets.

Histrionics aside, is the threat realistic? Or is it an exercise in wishful thinking?

"This isn't even a close question," said Laurence Tribe, a constitutional law professor at Harvard Law School, in an interview with CBSNews.com. "None of the executive actions President Obama has taken with respect to gun control could be said to violate the Constitution in any respect...Even to dignify the claim that his executive orders are unlawful, let alone impeachable, with a formal discussion is close to ridiculous."

Tribe, who once taught Mr. Obama as a law student at Harvard in the 1970s, was so dismissive of the impeachment threats that he turned the issue back on those raising it. "If anything in this context would be an abuse of the Constitution," he said, "it would be an attempt to treat the President's actions as impeachable offenses."

For congressional Republicans, raising the specter of impeachment may be less a credible threat and more an act of catharsis, a supremely dramatic expression of disapproval that soon evaporates.

The Constitution specifies that impeachment of a government official can only be undertaken in response to "treason, bribery, and other high crimes and misdemeanors."

It was a very restrictive list of offenses, meant to imbue impeachment proceedings with a sense of gravity not reserved for other forms of censure.

And accordingly, in the history of the United States, only 19 federal officials have been subjected to impeachment proceedings. Of those 19, only two were presidents. Both were acquitted.

Andrew Johnson, our 17th president, who oversaw the beginning of the Civil War Reconstruction era, was impeached in 1868 after defying Congress by replacing his secretary of war.

The outrage over the secretary's dismissal was a mere excuse, a proxy war for bigger issues. Johnson, a Republican, had been at odds with radicals in his own party over his lenient approach to the union's reintegration of southern states. Some in Congress wanted to punish them for seceding, but Johnson saw wisdom in a lighter touch.

One Republican member of the House at the time grumbled, "Sir, the bloody and untilled fields of the ten unreconstructed States...cry, if the dead ever evoke vengeance, for the punishment of Andrew Johnson."

But despite the high drama of the issues involved - a civil war, thousands of Americans dead, the end of slavery - Johnson evaded conviction by a single vote in the Senate. Not even the lingering recriminations of a civil war could unseat a president.

Over a century later, Bill Clinton was tried for impeachment between 1998 and 1999, accused of perjury after denying a sexual liaison with a White House intern. The House voted to impeach, largely along party lines, but the proceedings died in the Senate, which acquitted Clinton 55 to 45 after 10 Republicans joined all 45 Democrats in voting against impeachment.

Clinton's transgressions did not quite amount to "high crimes and misdemeanors," and no amount of Republican teeth-gnashing would change that.

The modern president who came closest to being impeached and removed from office was Richard Nixon in 1974, who resigned in the wake of the Watergate scandal. Nixon saw the writing on the wall, choosing to leave office instead of submitting to the ignominy of near-certain impeachment and expulsion.

The experience of these three presidents is a valuable reminder that, historically, impeachment is not a process our elected officials have approached lightly. It is not a trifle that has been casually tossed out at the first sign of a dissenting opinion or a controversial policy initiative. It is a rare and ultimate political punishment, and it is extraordinarily difficult to justify and execute.

And the founders, from the beginning, envisioned as much. "Experience has already shown that the impeachment the Constitution provided," Thomas Jefferson once said, "is not even a scarecrow."