An academic was the first to cross the invisible line.

"The ultimate check on presidential lawlessness is elections and, in extreme cases, impeachment," Georgetown law professor Nicholas Rosenkranz told Representative Darrell Issa at a House Judiciary Committee hearing Tuesday on the president's duty to uphold the law.

With that first mention of the "i word," leaks began springing from the dam that had been holding back the House GOP lawmakers united by frustration with President Obama's executive abuses. Republicans have been watching impotently as Obama has walked all over the law, with increasing brazenness the further he gets into his tenure. His first term included major clashes over Congress's subpoena power and, months before the election, the president's imposition of the "DREAM Act" by fiat - something he had publicly said before was beyond his legal authority.

Almost a year into Obama's second term, his unilateral delays of Obamacare and other legally questionable actions are now routine. He even threatened to veto a bill that would have ratified something he had done on his own without any clear authority, the delay of Obamacare's employer mandate.

"It's a real problem," House Judiciary Committee chairman Bob Goodlatte says. One of the biggest frustrations: Senate Democrats don't seem to give a rip.

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Seeking ways to limit the president’s executive overreach, Republicans still shy away from impeachment.

"To me, the Senate being complicit in watching the executive branch strip the powers of the Congress is absolutely despicable," Goodlatte tells me. "You don't hear a peep out of Harry Reid about the fact that prerogatives of Congress are being trampled upon by the executive branch." Following Issa's questions, Iowa Republican Steve King asked the expert witnesses what remedies Congress has for a president unbound by the law. Having dismissed the "power of the purse" as obviously ineffective (just look at the government shutdown, several lawmakers and witnesses pointed out), King moved on down the line to lawsuits and, finally, the remedy that shall not be named.

"Then the next recourse is, as Mr. Rozenkranz said, the word that we don't like to say in this committee and that I'm not about to utter here in this particular hearing," King said.

King tells me the next day he didn't want to distract from the president's actions by saying the word out loud. But the experts at the witness stand didn't shy away from radical ideas.

"There is a procedure in the Constitution that allows the people to amend the Constitution without going through Congress," the Cato Institute's Michael Cannon offered. "That is another method where the people can try to restrain the executive."

And Rozenkranz dismissed King's timidity, enunciating the word like a dare, loud and clear.

"I don't think you should be hesitant to say the word in this room. A check on executive lawlessness is impeachment. And if you find the president is willfully and repeatedly violating the Constitution. . . . I think that would be a clear case for impeachment," he said.

George Washington University law professor Jonathan Turley, a frequent guest of Keith Olbermann and Rachel Maddow during the Bush years, described the situation in severe terms.

"I really have great trepidation over where we are headed," Turley said. "We are creating a new system here. . . . The center of gravity is shifting, and that makes it unstable. Within that system you have a rise of an uber-presidency. There could be no greater danger for individual liberty. And I really think that the Framers would be horrified by that shift."

The situation, Turley later said, is the "most serious constitutional crisis, I believe, in my lifetime."

Then the dam burst altogether. Responding to a hypothetical from King about the president's declaring war without Congress's assent, Cannon raised the idea of revolution.

"I think what Mr. King was getting at is, there is one last thing to which the people can resort if the government does not respect the restraints the Constitution places on the government," Cannon said. "Abraham Lincoln talked about the right to alter our government or our revolutionary right to overthrow it. And that is certainly something that no one wants to contemplate. But as I mentioned in my delivered testimony, if the people come to believe that the government is no longer constrained by the laws, then they will conclude that neither are they. That is why this is a very, very dangerous sort of thing for the president to do - to wantonly ignore the laws, to try to impose obligations on people that the legislature did not approve."

"An excellent conclusion!" exclaimed King.

That said, in a phone interview, Cannon admitted he can't think of "anything" Obama could do in the next three years that would lead to rebellion. He regrets even mentioning it, he said, because it allowed people to impute a "nutty idea" to him (that today's circumstances are serious enough to prompt talk of violent overthrow of the government).

Nevertheless, the fact that the House Judiciary Committee is entertaining such dire discussion shows how wantonly the House GOP feels Obama has transgressed the law - and how eager they are for a way to stop him.

"I don't think he's pushed the legal envelope. I think he's shredded the legal envelope," says Representative Tom McClintock of California. One problem, McClintock laments, is that younger generations don't seem to be very upset about it.

"Ultimately it will come down to whether the owners of the Constitution insist that it be enforced with the votes they cast at the ballot box. So far this generation has been rather lax," he says.

Like most Republicans I speak with, McClintock says impeachment is not on the horizon. But the possibility does increasingly pop up in conversations with conservatives on and off Capitol Hill.

Issa, who is locked in a legal battle with Attorney General Eric Holder over the House's subpoena power, says impeachment is a "blunt instrument" and often an "inappropriate" one.

He points out that Holder, in arguing before a court that it did not have jurisdiction over the dispute, noted Congress has the power of impeachment as a possible remedy.

"That, in a sense, is a dangerous thing for a president to say. I don't know that objecting to a discovery order from the Congress is a high crime or misdemeanor," Issa says. "But if they take away the tool of court review, and suggest that we only have one tool, then like a carpenter who's only given a hammer, he'll use it."

"And, by the way, I have used a hammer to break a board in half because I didn't have a saw," Issa tells me.

Representative Lamar Smith of Texas, the previous chairman of the Judiciary Committee, offers this tantalizing explanation for his silence: "The reason I can't answer any impeachment questions is because any impeachment actions go through the Judiciary Committee, and I don't want to have to recuse myself."

The talk of impeachment and overthrow provoked predictable winces among GOP-leadership aides, and there is also a lot of residual disquiet about the tactic from the Clinton experience.

King, for example, notes the first time he set foot in the House Rayburn Office Building, in 1998, was to watch the Judiciary Committee impeachment proceedings against Clinton in person. Then a state senator, King watched as the Senate, in his view, perverted the process, lumping questions of whether Clinton was guilty of the charges in with the question of whether to remove him from office.

"That's not gonna happen. We've been through that with Bill Clinton. I saw that up close and personal. I think I understand the political dynamics that unfolded there. You'll never get an honest verdict out of the United States Senate if Harry Reid is going to be the majority leader," he says.

The GOP's most promising effort is the lawsuits pending in courts across the land. Cannon, for instance, is bringing a legal challenge to Obamacare, contending the law doesn't authorize subsidies or tax penalties in states using the federal exchange.

Simon Lazarus, the Democrats' legal witness at the Judiciary hearing Tuesday, struggled mightily to articulate a plausible defense against the argument.

Another Obamacare challenge is over the fact that the bill included tax increases but originated in the Senate. Under the Constitution, tax bills are supposed to start in the House.

The union representing federal employees who enforce the southern border have a pending lawsuit over Obama's unilateral DREAM Act.

Issa just won a round against Holder on the subpoena matter. And there are a good number of other suits.

Several legal victories in a row could snowball into momentum, bringing the public's attention to the issue. The Judiciary Committee hearing itself is a sign that the GOP is going to be taking Obama to the mat on his legal authority more than in the past.

In the meantime, though, the House GOP seems, at times, helpless to stop Obama. It's that sense - that they're flailing, and there are no other options - that could finally have Republicans confidently uttering the i-word.