The 64-year-old Romney, former Massachusetts' governor, ran well ahead of his three opponents during his second decisive first-place finish in four days, following his victory in the Florida primary on Tuesday.
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With nearly 47 per cent of Nevada votes counted, Romney had 42.6 per cent of the vote followed by 26 per cent for Newt Gingrich, former Speaker of the House of Representatives. Texas Representative Ron Paul was third with 18.5 per cent, followed by Rick Santorum, a former US senator from Pennsylvania, with 13 per cent.
Romney thanked supporters at his campaign headquarters in Las Vegas, telling them that, "This isn't the first time you gave me your vote of confidence, but this time I'm going to take it to the White House," alluding to his win in Nevada in 2008. But then he turned his attention to Obama, saying Nevada has had enough of his kind of help in fixing its home mortgage crisis and that he failed at bringing down unemployment, saying, "America has also had enough of your kind of help."
"This president's misguided policies made these tough times last longer," he said. "We won't settle for a president who tells us it could be worse. What defines us as Americans is our unwavering conviction that things must be better. That conviction guides our campaign. It has rallied millions of Americans to our cause, including tens of thousands of Nevadans who gave me their support today," Romney said.
Romney said his campaign is about more than replacing a president. It is about saving the soul of America, he said, adding President Obama wants to "fundamentally transform" America. "We want to restore America to the founding principles that made this country great. Our vision for the future could not be more different than his," he argued.
The votes are the latest stage in the state-by-state process of picking a Republican nominee to challenge Democratic President Obama in November's general election.
Romney said Obama "will grow government and amass more trillion-dollar deficits. I will not just slow the growth of government, I will cut it. I will not just freeze government's share of total economy, I will reduce it. And, without raising taxes, I will finally balance the budget," he said.
Obama's "brand of capitalism sends your money to his friends' companies. My vision for free enterprise is to return entrepreneurship to the genius of consumer markets and to the creativity of the American people," he said. He alleged that Obama demonises and denigrates almost every sector of US economy.
"I will make America the most attractive place in the world for entrepreneurs, for innovators, and for job creators. And unlike the other people running for President, I know how to do that. If elected President, my priority will be worrying about your job, not saving my own," Romney said.
All of Romney's three opponents, despite their defeat, vowed to continue their political battle against him. Gingrich said he will remain in the presidential race all the way to August, adding that he hopes draw equal with frontrunner Mitt Romney in delegate numbers by April. "We will continue the campagn all the way to Tampa," he said, referring to the Republican Party convention, which takes place in the Florida city in August.
The Republican candidates are fighting to win the most of the 1,144 delegates in Tampa. So far Romney has 95, Gingrich 30, Paul 13 and Santorum 10.