Washington (CNN) -- "Read my lips." "Mission accomplished." "Definition of 'Is'"
Every modern president has got one -- an inelegant statement, a broken promise, or an outright steaming lie, distilled to a three-second sound bite, that follows them into history.
It can be part of a campaign slogan, a policy address or legal testimony.
It can be delivered at a party convention, as part of a stump speech, from an aircraft carrier or during a deposition.
It can be well-intentioned, misinformed, only untrue after the fact. And the facts can be entirely debatable.
But there seems to be a lie or two that follows presidents into the history books. Here is a look at some recent memorable ones:
He's got some time in office left, but Barack Obama's signature gaffe line probably is going to be: "If you like your health insurance, you can keep it"
It was a key line in selling the Affordable Care Act, which narrowly passed back in 2010. But he has said it since then, too.
What he said was true for most Americans. They get their health insurance through their employer or the government with Medicare.
But as open enrollment began this month for the fewer than 20% of Americans Obamacare was designed to help, it became clear there is a subset of people who like their health plans and will in fact lose their health plans.
These are the subset of Americans who buy their insurance individually and, because those plans don't cover everything Obamacare now says must be covered, will have to get a new health care plan.
Granted, it might be a better health care plan. It might cover more services, like hospital stays, maternity, and mental health. But it also might be more expensive.
Obama tweaked the promise after the fact during an appearance in Massachusetts on Wednesday. But it's not exactly going to fit on a bumper sticker any more:
"Now, if you had one of these substandard plans before the Affordable Care Act became law and you really liked that plan, you're able to keep it," Obama said this week. "That's what I said when I was running for office. That was part of the promise we made. But ever since the law was passed, if insurers decided to downgrade or cancel these substandard plans, what we said under the law is you've got to replace them with quality, comprehensive coverage -- because that, too, was a central premise of the Affordable Care Act from the very beginning."
"And today, that promise means that every plan in the marketplace covers a core set of minimum benefits, like maternity care, and preventive care, and mental health care, and prescription drug benefits, and hospitalization," Obama explained. "And they can't use allergies or pregnancy or a sports injury or the fact that you're a woman to charge you more. They can't do that anymore. They can't do that anymore."
George H.W. Bush's was the most devastating. "Read my lips," he declared at the 1988 Republican National Convention. "No new taxes!"
It was a campaign pledge. And he broke it, big time.
Bush didn't want to break the pledge, but in the face of a recession, and to avoid $100 billion in automatic, across-the-board spending cuts, he acquiesced and allowed a tax hike on the wealthy.
It was disastrous for Bush. It created a rift in the GOP and directly led to a spirited primary challenge two years later by Pat Buchanan.
Bush ended up winning the primary, but losing re-election in a three-way race against Bill Clinton and Ross Perot.
George W. Bush never said, "Mission Accomplished," but the banner placed behind him did when he landed on the deck of the USS Abraham Lincoln in a Navy jet and declared that "major combat operations in Iraq have ended."
They hadn't. In fact they were just getting started. And Bush would have to stake his legacy on a subsequent surge of American troops in Iraq. Bush won re-election in 2004, but the war cost America a great deal in blood and treasure. Fatigue with Iraq contributed greatly to Republicans' losing control of Capitol Hill in 2006.
Some presidents have more than one. The younger Bush will also be remembered for his decision to use public unity following the 9/11 attacks to mount a war in Iraq, and the 16 words he used to justify the action.
The case Bush made in his 2003 State of the Union address helped lead the United States into Iraq. He said, "The British government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa."
It wasn't true.
But that didn't become clear until later after a high-profile scandal involving the leaking of CIA agent Valerie Plame's identity by Vice President Dick Cheney's chief of staff. But the point of the 16 words, more importantly, is that the intelligence used to convince the country that combat operations were necessary to stop the spread of weapons of mass destruction was inherently flawed.
And not to pile on Bush '43', but in the days just after Hurricane Katrina devastated the Gulf Coast and left much of New Orleans under water, the president came under intense heat for what was seen as a lackluster response by the federal government.
On September 2, 2005, just three days after Katrina destroyed the levees and flooded much of New Orleans' Ninth Ward, Bush heaped unusual praise on then-FEMA director Michael Brown during a briefing at the Mobile Regional Airport.
The soundbite, "Brownie, you're doing a heck of a job," would haunt the president and go on to define a perception that Bush was out of touch during one of the worst tragedies in American history.
Whitewater independent counsel Ken Starr wasn't originally appointed to investigate Bill Clinton's Oval Office sex life. But somehow that's what it turned into. And without getting too far into the sordid details, the President found himself giving a videotaped deposition in a case regarding sexual harassment charges.
The whole definition of sexual relations and the word "is" became a thing, the President faced impeachment and was nearly thrown out of office.
He survived, but his legacy and his agenda were tarnished.
And the list goes on.
Ronald Reagan had to admit he didn't know about the Iran-Contra affair. Jimmy Carter talked to the nation about a "crisis of confidence" and was panned for giving a "malaise" speech. And Gerald Ford's contention in a debate with Carter that "There is no Soviet domination of Eastern Europe" made him look oblivious to the Soviet Union's political and military control of the region.
There are some rules that emerge. If the moment has to do with the economy and it occurs in the first term, there's a good chance the president won't make it to a second term. If it has to do with foreign affairs, it might be just a blip on their legacy.
The good news for Obama is that he's been through his last election. The bad news is this demonstrably false new line has everything to do with his signature health law.
As it carries on, how Americans react to the implementation of Obamacare could have real consequences on whether his successor is a president who wants to make the law better or gut it.