In the week leading up to the South Carolina Republican primary, GOP presidential candidates furiously accused each other of "lying" - a term that was once rarely uttered by those running for the country's highest office. (Sarah Parnass/The Washington Post)

GREENVILLE, S.C. — A photograph posted on a website by Ted Cruz’s presidential campaign this week appeared to show his rival, Marco Rubio, shaking hands with the dreaded Democratic president, Barack Obama.

The picture, though, was a fake — a crude photoshop image of Rubio’s head posted on another person’s body.

“This is how phony and how deceitful the Cruz campaign has become,” Rubio adviser Todd Harris told reporters here, alleging that Cruz has “created a culture of lies.”

In the Republican presidential contest, 2016 has become the year of the liar.

Republican presidential candidate Ted Cruz speaks during a campaign rally in Charleston, S.C. (Jim Watson/AFP/Getty Images)

Once considered the semantic equivalent of tossing a grenade, use of the word has become routine among Republicans vying for the presidential nomination and their staffers. Candidates accuse one another of lying. They defend themselves from accusations of untruths. During the last Republican debate, “liar” or some variant was used at least 20 times.

“For a number of weeks now, Ted Cruz has just been telling lies,” Rubio said during the debate. “He lied about Ben Carson in Iowa. He lies about Planned Parenthood. He lies about marriage. He’s lying about all sorts of things.”

The language this year, including the liar tag, seems notably coarser than in past election cycles. Hearing words once considered off-limits is no longer strange.

“I certainly can’t recall anything like what we’re hearing now,” said Mark Liberman, a professor of linguistics at the University of Pennsylvania.

Among the many rough words and phrases used by GOP candidates to describe their opponents this cycle are “pussy,” “jackass” and “unstable.” But liar seems to have the most staying power.

“It’s clearly a blow to the civility of the election discourse,” said William Mayer, a professor of political science at Northeastern University.

Republican presidential candidate Donald Trump speaks during a campaign stop in South Carolina Monday. (Matt Rourke/AP)

Rarely a day goes by now that the word is not used. Frustrated by the tenor of the debate, the conservative Weekly Standard wrote that the candidates should try a new variation of Ronald Reagan’s famous 11th commandment that “thou shalt not speak ill of any Republican.”

“The Republican presidential field could at least try to observe a twelfth commandment: Thou shalt avoid calling one’s fellow Republican a liar,” the magazine wrote.

For the most part, the epithet has been hurled against Cruz, who is in a heated race for second place here with Rubio and has faced repeated accusations of lying from both Trump and Rubio.

“He is a liar,” Trump said of Cruz in a statement released Wednesday. Pointing at Cruz during the debate Trump said, “You are the single biggest liar.”

At a rally Friday in Myrtle Beach, S.C., Trump went after Cruz again.

“This Ted Cruz, this is the biggest liar,” he said. “...Even Marco Rubio said he’s a liar... This guy, Ted Cruz, is a liar.”

Trump has also uncorked the word on former Florida governor Jeb Bush.

“I’d like to call JEB a liar, but the truth is he has no clue & never revealed that he used Eminent Domain- when criticizing me!” Trump wrote on Twitter.

Politicians calling one another a “liar” has happened in the past, most recently

Prior to the current race, perhaps the most well known use of the liar charge by a politician came in 2009, when Rep. Joe Wilson (R-S.C.) yelled “you lie!” at President Obama during the State of the Union address. Wilson was booed and formally rebuked by the House in a vote that fell largely along party lines; he refused to apologize.

Using the word once had far more dire consequences: a duel. According to the Encyclopedia of Arkansas History and Culture, in 1827 Henry Conway, who was running for reelection to Congress, called Robert Crittenden, the acting governor of the state, a liar in a published letter. The two men had a duel and Conway died from his wounds 11 days later.

When asked about use of the word “liar,” Cruz supporter and House member Steve King (R-Iowa) said: “Aaron Burr and Alexander Hamilton fought a duel to the death over such allegations, and now we have them hurled out as if making that allegation somehow makes it true and makes it stick.”

Mayer said calling someone a liar raises the stakes and implies something harsher than simple disagreement.

“I’m implying very different things about an alternative candidate if I say ‘you’re lying’ or ‘I disagree with you’ or ‘you’re mistaken,’” he said.

Richard D. Anderson, Jr., a professor of political science at UCLA who has studied political linguistics, said the tone has something to do with the dynamics of the race, including the public’s distrust of career politicians.

The word liar, Anderson said, is “evoking people’s anger and unhappiness with fellow politicians.”

Rubio has long accused Cruz of distorting the truth, but the Florida Republican’s campaign said the argument has only broken through this week as Rubio and Trump have focused on it. Trump’s accusation at the debate that Cruz is a liar amplified the message before a broad audience like never before.

“He’s lying — and I think it’s disturbing,” Rubio told reporters this week before hopping on his campaign bus in Beaufort, S.C.

Rubio added: “Just here in South Carolina this week, he’s lied about my record on Planned Parenthood, he’s lied about my position on marriage, he’s lied about his own record on immigration, and so I think this is very disturbing when you have a candidate that now on a regular basis just makes things up. And especially in this era where everything is out there and everything is seen and instantly reacted to, you can’t get away with that stuff.”

Jason Miller, a spokesman for Cruz, said the word “liar” has become the “only message” from Trump or Rubio.

South Carolina Gov. Nikki Haley, when asked about whether the pervasive use of the word would turn off voters, said people here know how to cut through the mud of this state’s rough and tumble campaigning.

“When you come to South Carolina, it’s a bloodsport,” she said. “I wear heels, it’s not for a fashion statement. It’s because you’ve got to be prepared to kick at any time.”

But some voters don’t like it. When asked about the use of the word liar, Carrie Williford, who was attending a Ted Cruz rally in Spartanburg, S.C., made an annoyed face.

“The word is overused,” the 37-year-old from Greer, S.C., said. “It sounds like fifth grade schoolyard type stuff.”

Jenna Johnson contributed reporting from Myrtle Beach, S.C., and Sean Sullivan from Beaufort, S.C.