In the blink of a news cycle, the Republican campaign has turned nasty.Ronald Reagan’s famed 11th commandment is toast.Newt Gingrich called Mitt Romney a “liar,” and Rick Santorum called Ron Paul “disgusting.”Feeling the pressure much?Newt’s attack makes tactical sense, though for a guy who’s been complaining about negativity and trumpeting the virtues of a positive campaign, he risks coming across not just as harsh but petulant. Santorum’s attack makes no sense.In Gingrich’s case, yes, he was responding to a Norah O’Donnell question on CBS’s Early Show, but he chose to embrace the L-word. (Gingrich is looking angry these days, but he has a point: Reporters haven’t pressed Romney on why he won’t even express disapproval while a PAC staffed by his loyalists dumped more than $3 million in negative ads on Newt’s head.)So how is Mitt lying? “Do you really want a Massachusetts moderate who won’t level with you to run against Barack Obama who, frankly, will just tear him apart? He will not survive against the Obama machine.” The charge goes to the core of the Romney candidacy, suggesting the evolution from his pro-choice, pro-gay rights days is entirely inauthentic. This may be the only argument that could enable Gingrich to overtake Romney if the former speaker survives Iowa. But it also reminds people of Neutron Newt and his history of overheated rhetoric (Democrats are the “enemy of normal Americans” and so on).As for Santorum, why is he wasting his artillery on Paul? Yes, he’d like to finish ahead of the Texas congressman in the caucuses, but it’s virtually impossible for Ron Paul to win the GOP nomination—even Paul says he doesn’t envision himself in the Oval Office.According to FoxNews.com, Santorum was responding to reports of robocalls that accused the former senator of being pro-choice and against the Second Amendment. Santorum has every right to denounce such attacks; as John Kerry learned, it can be fatal to stay silent while unfair charges are hurled at you. But if Santorum indeed called Paul disgusting, he risks coming off as a schoolyard bully and alienating Paul sympathizers who might be persuaded he’s a more viable choice.At this stage of the game, the candidates are tired, frustrated and a bit prickly (except for Romney, who still has every hair in place). That’s when you say things you might soon regret.