WASHINGTON (CNN) -- In a season when words are weapons, it's the H-bomb of campaign trail rhetoric -- a word so potent that a single appearance usually sparks days of cable debate and a sea of news ink.
Mistaken, evasive, misleading, wrong -- all language that leaves room for good intentions or honest differences of opinion.
Not the L-word. It's a rhetorical bludgeon: Not only is your opponent off base, he's deliberately deceiving the public. It's a bruising character judgment that leaves minimal room for error.
But as Sen. John McCain and Alaska Gov. Sarah Palin hit the trail together in the first full week of the general election campaign, the Obama campaign has begun using "lie" -- and its cousins, like "falsehood" -- against the pair with such regularity that the appearance of these words has become almost routine.
On Monday, the campaign sent supporters an "Obama action wire" titled "Lying on the Record." In case readers missed the subject line, the first paragraph repeated the rhetorical depth charge: "The McCain campaign is lying about their candidates' records," it read.
The same day, the campaign took the word to the airwaves. "Politicians lying about their records?" asked an announcer in an Obama ad released this week, over an image of the Republican nominee and his running mate. "You don't call that maverick. You call it more of the same."
And campaign staffers used the word on the record. "Despite being discredited over and over again by numerous news organizations, the McCain campaign continues to repeat the lie that Sarah Palin stopped the 'Bridge to Nowhere,' " Obama spokesman Bill Burton said Monday.
Sometimes members of Obama's staff have distanced themselves from the word even as they use it, attributing the claim to third parties.
"On the same day that dozens of news organizations have exposed Gov. Palin's phony 'Bridge to Nowhere' claim as a 'naked lie,' she and John McCain continue to repeat the claim in their stump speeches. Maybe tomorrow she'll tell us she sold it on eBay," Obama campaign spokesman Tommy Vietor said, pointing to a quote from The New Republic.
Obama danced around the accusation for days, moving closer to a direct charge.
"I mean, you can't just make stuff up," he told the crowd at a campaign event earlier this week. "You can't just re-create yourself. You can't just reinvent yourself. The American people aren't stupid."
But he eventually embraced the word, using it Wednesday to blast the McCain campaign for its "lipstick on a pig" attacks.
"I don't care what they say about me," Obama said. "But I love this country too much to let them take over another election with lies and phony outrage and swift boat politics. Enough is enough." Watch Obama's heated words for the Republicans »
The word "lie" is "a powerful weapon," said Georgetown University professor Stephen Wayne, an expert on the presidency -- particularly against a politician like McCain, whose success is rooted in his "straight-talk" image. But that image also provides the Republican nominee with unusually effective armor.
"The Obama campaign could be wasting their time," Wayne said, because the accusation could ring hollow.
"People have already formed a judgment of McCain. But not Obama. If they're not careful -- if McCain is wrong on a claim, but can plausibly say it wasn't deliberate -- it could backfire," Wayne said. "You're making a statement about intent, and you're going to have to back it up. It will be hard to get McCain on that," he said.
But McCain's running mate, likely the true target of the latest blitz, might be more vulnerable.
"I don't think people know enough about Palin to form a judgment about her," Wayne said.
And as the charge becomes routine, the Obama camp isn't alone in using it: The McCain team is lobbing the grenade back.
Responding to Obama campaign assertions that Palin wasn't always the pork-barrel spending opponent that she claims to be, McCain spokesman Brian Rogers said, "The only people 'lying' about spending are the Obama campaign."