Candidates prep for televised debates Barack Obama and Mitt Romney have spent months attacking one another from afar. But when they take the stage for their first presidential debate in Denver next week, it will mark the first time the two rivals have faced each other directly. For both candidates, the intense preparation for this potentially pivotal occasion is as much a study in psychological warfare - of knowing what gets under your opponent's skin - as an exercise in debating policy. They will spend this weekend fine-tuning their strategies and practising the zingers they hope will define the other in voters" minds or, in the case of Mr Romney who is lagging in the polls, prompt voters to give him a second look. In the history of US elections, there have been occasions when a candidate's gaffe or physical appearance, like Richard Nixon's sweaty face-off against John F. Kennedy, and George HW Bush's glance at his wristwatch in his matchup against Bill Clinton, have been harmful. Those practised in helping politicians prepare for such debates say understanding their opponent's vulnerabilities is crucial. They say the candidates and their prep teams will be strategising about what might trigger Mr Obama to look too aloof, and not just cool under pressure, or what line of attack will get Mr Romney agitated and off his script. David Smith, a Democratic congressional aide who played Mr Romney when preparing his former boss, Ted Kennedy, for the late senator's 1994 debate against the Republican, noticed the challenger had "a very hard time" with follow up questions, which Mr Smith now attributes to Mr Romney's "extraordinary arrogance." "He resents being pressed because he thinks he has told you what he wants to tell you and doesn't understand why you aren't satisfied," Mr Smith says. Kennedy was able to use that to an advantage. In an interview last year with Fox News's Bret Baier, Mr Romney impatiently chided the reporter for repeatedly drilling him on his healthcare policy. The Republican candidate snapped that it was an "unusual interview." Mr Romney's privileged lifestyle and upbringing also create the risk that he appear out-of-touch with average Americans. During the Republican primaries he famously challenged Texas governor Rick Perry to a $10,000 wager, as if that figure amounted to pocket change. His authenticity will be judged against the "47 per cent" video that was recently released, showing him disparaging nearly half the electorate as too dependent on government. Democrats also see a lack of detailed plans from Mr Romney as a weakness. "My guess is that Romney is even more vulnerable because he has had to contort himself so much to pursue what he thinks the objective is, which is getting elected," says Mr Smith. Mr Obama too his weak spots. Although he is a gifted orator, he has a tendency to drift into his old role as law professor when confronted with complex questions, instead of keeping to sharp and concise responses. "He's got his own verbal tics," said one former senior Democratic Senate aide, pointing to the long pauses used in comedic renditions of the president. "He has a kind of speaking in the abstract that means that his answers can be convoluted and overly lengthy," said Alan Schroeder, an expert on presidential debates at Northeastern University. He can also appear arrogant and smug, such as when he interjected that Hillary Clinton was "likeable enough" when she was asked in a primary debate about her "likeability." He barely looked up from his notes as he said it. Mr Romney's aim will undoubtedly be to keep Mr Obama from talking about the future and on the defensive, using his record on the economy and his words against him, such as when Mr Obama promised in 2009 that he would be held "accountable" if he did not cut the deficit in half in his first term in office. Mr Romney will practise with Rob Portman, a stand-in for Mr Obama during the last presidential contest with John McCain of Arizona. Mr Obama will practise his sparring with John Kerry, the Massachusetts senator and a sharp and experienced debater who happens to exude the same patrician comportment as the man he is playing.