The two men touted as Republican frontrunners - Rick Perry and Mitt Romney - resisted, with great difficulty, an urge to get into a physical fight during a tense GOP presidential debate on Tuesday.

In the midst of a heated verbal sparring session, Romney apparently tried to physically intimidate his opponent by placing a hand on his rival's shoulder, after being visibly annoyed by the Texan's repeated interruptions.

Within 40 minutes of Tuesday's CNN debate in Las Vegas, the verbal war between Romney, the former Massachusetts governor, and Perry became personal, with both candidates trying to portray the other as a hypocrite.

While Romney accused Perry of signing legislation which put in place a magnet to draw illegals to Texas by offering college tuition, Perry shot back, alleging that Romney hired illegal immigrants to mow his lawn a few years ago.

So we went to the company, and we said, 'Look, we can't have illegals working on our property. I'm running for office, for Pete's sake. I can't have illegals, said Romney, explaining the incident. 

Though Romney appeared to win the verbal clash, the shoulder touch employed seemed to be dripping with the idea to intimidate, a rare gesture in an American political debate.  

Invading a rival's personal space is the least polished winning tactic, even though it has been employed by many candidates in the past.

In September 2000, Republican Senate candidate Rick Lazio shoved a campaign pledge at rival Hillary Clinton, demanding her to sign it, in an act aimed at intimidating her. In the following month, George W. Bush offended then-Vice President Al Gore, who walked over to his podium. Bush cut him down with a curt nod.

Though Romney's shoulder touch has been perceived by some viewers as unwarranted, many thought he was simply trying to calm Perry down.

It's Romney, the elder statesman, putting his hand on a hothead's shoulder and saying, 'Son, calm down,' Stanley Renshon, a prolific author of books on politics and psychology, told the Los Angeles Times.

Perry came across as being too rough. If any of my students had done that, I would have taken them to the woodshed, said Matt Towery, an Atlanta-based nonpartisan pollster and onetime debate champion.

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