Mitt Romney fiercely mocked President Barack Obama as Republicans blitzed Iowa, a week before the first votes of the 2012 White House race are cast in the US state's fabled caucuses. Longtime national front-runner Romney launched a three-day bus tour after his campaign's barrage of negative advertising appeared to slow a surge by former House speaker Newt Gingrich. As time runs out before the January 3 Iowa caucuses, the former Massachusetts governor took direct aim at Obama, the man the Republican rivals are vying to take on in November's general election. "Four years ago this week Barack Obama ... promised to bring people together," Romney said in Davenport, Iowa, riffing off a speech that the then senator Obama gave in the same town during his 2008 presidential run. "He promised to change the broken system in Washington. He promised to do away with gridlock. He promised to repair the nation. "He promised to put Americans back to work. He closed with these words: 'This is our moment, this is our time.' "Well Mr President, you have now had your moment. We have seen the results. And now, Mr President, it is our time." Romney is fighting Gingrich, libertarian congressman Ron Paul and rising outsider Rick Santorum among others in caucuses which open months of votes to produce a nominee who will seek to deprive Obama of a second term. His speech represented a clear attempt to paint himself as a prohibitive frontrunner and the most electable potential nominee to face Obama. "Gone is the 'hope and change' candidate of Davenport," Romney said. "Gone is the candidate who would heal the nation. Instead, the campaigner in chief divides Americans, engages in class warfare and resorts to distortion and demagoguery. "Once, Barack Obama appealed to our better angels; today he demonizes fellow Americans." Gingrich, who faces questions about whether his rudimentary political organization will turn out the vote in Iowa, launched an outspoken counter-attack on Romney and Paul, who have been dragging up his past. He complained that Romney's campaign had distorted the truth regarding $1.6 million his consultancy was paid as an advisor to troubled government-backed mortgage giant Freddie Mac. "He knows better. His staff knows better," Gingrich told CNN, saying his firm got the money and he only saw a fraction of it. Gingrich also lashed out at critics who say he is inconsistent on illegal immigration and government-run health care, explosive issues in Republican politics. And he slammed Paul for what he said was a record of "systemic avoidance of reality" on foreign policy, including on the September 11 attacks in 2001 and Iran. He also used the CNN interview to brand Obama as somebody who says "I don't care if Israel's destroyed. I don't care if the Iranians get a nuclear weapon," twisting Obama's comments and policy on Tehran's nuclear program. According to a RealClearPolitics average of recent Iowa polls, Paul leads the Iowa race with 22 percent, a point ahead of Romney, with Gingrich languishing back in third with 15 percent. Some recent surveys have also suggested that former senator Santorum, who is popular with evangelical voters, who are important in Iowa, was gathering momentum. But the Pennsylvanian was back on eight percent in the polling average. Polls also show the conservative vote split between several candidates including Santorum, Representative Michele Bachmann and Texas Governor Rick Perry. Such a scenario could help Romney, who has struggled to get his approval ratings above the mid 20 percent range in national polls despite being the best financed and most establishment candidate in the Republican race. A surprise win for Romney in Iowa, which helped doom his 2008 race, and in the New Hampshire primary on January 7, where he has a wide lead, could set up him for a decisive run in subsequent contests in South Carolina and Florida. But setting expectations are key in Iowa and his campaign has been careful not to put all its chips on the state, to give him plausible excuse if he were to founder in the caucuses. Iowa is not always decisive in nominating races -- John McCain did poorly here in 2008 but still won the Republican nod -- but it can winnow down the field. The state, snow covered in winter and bathed by golden corn come summer, can also launch famous political careers. Obama's triumph in the state over Hillary Clinton in 2008 set him on the road to the White House. Around 120,000 to 150,000 Republican voters are due to declare their presidential pick during the 1,774 caucus meetings next week