As the race for the Republican presidential nomination gets heated, White House bidders exchanged fire in a new round of debate Tuesday night, with two current front-runners -- Mitt Romney and Herman Cain -- drawing most of the bullets. Seven Republican presidential candidates -- former Massachusetts Governor Mitt Romney, Texas Governor Rick Perry, former Godfather\'s Pizza CEO Herman Cain, Minnesota Congresswoman Michele Bachmann, former House Speaker Newt Gingrich, Texas Congressman Ron Paul and former Pennsylvania Senator Rick Santorum -- appeared on the stage of the debate in Las Vegas, Nevada. With a rapid rise in recent national polls to become one of the front-runners, Cain came to be the focal point immediately after the debate kicked off. Almost all the rivals on the stage criticized his signature 9-9-9 plan to replace the current tax code with a 9 percent rate for personal income, corporate and sales taxes. The outcome was well expected as the rising poll numbers put Cain under more scrutiny. A new CNN poll showed that Cain has seen his Republican support nearly triple, from 9 percent in September to 25 percent, almost tied with Romney who leads the race with 26 percent of support. Romney was under a fierce assault from his opponents on issues of healthcare and immigration. Critics have repeatedly associated the Massachusetts healthcare reform during Romney\'s governorship with that of the Obama administration, questioning his credibility as a real conservative. \"Governor Romney, you don\'t have credibility when it comes to Obamacare,\" Santorum said. \"Your plan was the basis for Obamacare. To say you\'re going to repeal it -- you have no track record on that we can trust you that you\'re going to do that.\" Romney defended his record by saying that the measure was something crafted only for his state and may not be a good policy on a national scale. \"The people of Massachusetts like it by a three to one margin,\" he argued. A more heated exchange of fire occurred between Romney and Perry on the issue of illegal immigrants. Perry accused Romney of hiring illegal immigrants and being hypocritical for his hard-line immigration stance. Romney denied the charges and fired back by saying he understood Perry\'s getting \"testy\" because \"this has been a tough couple of debates\" for him. Since the current debate season kicked off in September, Romney seemed to have been mostly unscathed even though he was in the crosshairs at most of the debates. Judging by poll numbers and fund-raising results, Romney is so far the most recognized front-runner in the Republican field