THEY call it Ronald Reagan's 11th commandment: never speak ill of a fellow Republican. For much of 2011 Republican contenders for the presidential nomination tried to keep the commandment at least half in mind. During the long sequence of televised debates they have made sure to smile and smile, even while shooting villainous little darts at one another. In mid-December, however, after Newt Gingrich sped ahead of Mitt Romney to become the front-runner, the darts turned into bullets. Each man is now doing his best to shoot gaping holes in the other's reputation. For the embattled presidency of Barack Obama, this is Christmas come early. In theory, primaries are all the better for being feisty affairs. The party will in due course unite around a hardened winner whom the primaries have tested along the way. But it can be hard to tell when a feisty primary is in danger of turning voters off all the candidates, to the benefit of the other side. This is a danger Mr Gingrich in particular has talked about from the start. He says frequently that any of the Republican candidates would be a better president than Mr Obama. He accuses the media of fanning artificial discord. And on December 13th, after one especially bitter rally of insults with Mr Romney, it was Mr Gingrich who tried to call a truce. He sent a letter to supporters and staff calling it “critical” for a Republican nominee to emerge unbloodied, the better to take on Mr Obama from a position of strength. For his part, he would eschew negative ads and run a “respectful and constructive” campaign, though reserving his right to respond when his record was “distorted”. A fine sentiment. But it may be no coincidence that it is Mr Gingrich who seems keenest to avoid negative campaigning. With his adulteries, flip-flops and the fortune he made by peddling influence in Washington, DC, the city that in Republican eyes has morphed from a mere capital into a modern Gomorrah, the former Speaker makes a juicy target. Mr Gingrich could be ignored when he was an also-ran, but now that he is rising it has become imperative for Mr Romney to knock him back before he does well not only in first-voting Iowa but also a week later on January 10th in New Hampshire, which Mr Romney had until recently seen as his “firebreak” against a rival with momentum.

On December 12th Mr Romney bowed to this imperative by calling on Mr Gingrich to return the $1.6m in fees he collected from Freddie Mac, the government-supported mortgage company he later excoriated for pumping up the bubble that helped cause the financial collapse of 2008. Mr Romney's people note that although Mr Gingrich demanded that Mr Obama should return his 2008 campaign donations from Freddie Mac, he refrained from criticising the organisation until his own lucrative contract with it was over. They call him “an unreliable leader” who went to Washington to do good but “stayed to do well”. Before proposing his truce, Mr Gingrich fired back by saying that he would listen to Mr Romney if the former venture capitalist gave back “all the money he's earned from bankrupting companies and laying off employees over his years at Bain”.

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Mr Romney paints Mr Gingrich as a hypocrite who talks about small government but has grown rich by milking the taxpayer. Mr Gingrich paints Mr Romney as a heartless plutocrat. Even the professorial Ron Paul, the indefatigable libertarian from Texas, has abandoned his avuncular pose and decided that this is the time to slash at the Gingrich jugular. Vicious ads by Mr Paul are running in Iowa, where he has a strong organisation and an avid following, blast Mr Gingrich's “serial hypocrisy” and denounce him as “a career politician” who “sold access” in Washington. The ads brim with incriminating footage: Mr Gingrich sitting alongside the Democrats' hated Nancy Pelosi, warning of the dangers of climate change; the tribune of the people bragging about his speaking fees of $60,000 a pop. A voice-over recalls that Mr Gingrich once supported the individual health mandate (compulsory medical insurance), the big idea at the centre of “Obamacare”, which Mr Romney also embraced when he was governor of Massachusetts but which is now Exhibit One in the Republican charge that Mr Obama is a socialist.

Are such attacks still just “feisty”, or might they damage the whole Republican brand in 2012? The party is not yet remotely as divided as it was in 1964, when its moderate wing refused to rally around Barry Goldwater when he became the nominee. It is worth remembering that the smears that soured the South Carolina primary fight between George Bush and John McCain in 2000 did not stop the Republicans from squeaking to victory in the end. Moreover, the Democrats still face an uphill struggle. A USA Today/Gallup poll from a dozen swing states shows that despite the recent uptick in the economy Mr Obama is trailing Mr Romney by 43% to 48% and even the baggage-laden Mr Gingrich by 45% to 48%. The proportion of voters who call themselves Democrats or Democratic-leaning in these states has fallen by 4% since 2008, while the Republicans have gained 5%.

That said, Mr Obama has the luxury of knowing that the Republicans are his only enemy, whereas it is hard to see how Jim Messina and David Axelrod, the strategists plotting the president's re-election from his campaign headquarters in Chicago, could invent more hurtful attacks than those the Republican candidates have started to fling at themselves. And it could get worse. Until recently, Mr Romney looked set to clinch a victory early, leaving ample time for him to train his fire on Mr Obama. Now it looks as though the Republicans might be in for a longer and more divisive primary campaign, with a less certain outcome. They need someone to be standing at the end of it.

Economist.com/blogs/lexington