Washington: As Republicans kicked off the primary battle to pick the candidate who will challenge Barack Obama, the incumbent President had a reassuring message for his supporters -- "I am more optimistic than in 2008".

Four years back, Obama launched his bid for the White House, before going on to win a historic victory, and despite a slide in his popularity over the period; the president said he was more confident heading into his second presidential battle having fulfilled some of his key promises.

"We have done a lot but we've got a lot more to do, and that's why we need another four years to get it all done," Obama said, when asked "how do you respond to people who say you haven't done enough?"

"In some ways, I'm actually more optimistic now than I was when I first ran, because we've already seen change take place," Obama said when asked if in 2012 he still believed in his 2008 war cry of hope and change.

Seeking a re-election in November, Obama asked his supporters today to gear up for the big battle ahead.

"It's going to be a big battle. I hope you guys are geared up. I'm excited," Obama said in his video address to the Democratic Party Iowa Caucuses goers.

Obama touted the end of the war in Iraq, health care reform and making college more affordable as some of the achievements of his tenure.

He also said everybody deserved a "fair shot," while attacking the Republicans for supporting "tax cuts for the wealthiest among us".

In Iowa, meanwhile, the Republicans saw a tight three-way contest among their White House hopefuls, with former Massachusetts Governor Mitt Romney and former Pennsylvania Senator Rick Santorum deadlocked for the lead and Texas Congressman Ron Paul close behind.

Obama said his campaign for 2012 will focus on the benefits his administration had brought in the health and education sector.

"Part of what 2012 is about is both reminding the American people of how far we've traveled and the concrete effects that some of our work has had in terms of making sure that people have health insurance, or making sure that our troops are coming home, or making sure that young people are able to go to college.

"But part of it is also framing this larger debate about what kind of country are we going to leave for our children and our grandchildren," he said.

Obama said while problems affronting the country can be solved, it is also to be ensured that everybody gets a fair shot while addressing collective concerns.

However, Obama has a tough battle at hand to reclaim the White House in the face of a dull economy and high rates of unemployment, results of the economic recession the President has struggled to deal with ever since assuming office.

And Obama is certainly aware of the fact that the downsides are overshadowing his achievements.

"But we all know we've got a lot more work that we have to do," he noted.

Giving every section a fair shot means that "we're investing in things like education, that we're investing in basic science and technology so we're making things again here in America and we're revitalising manufacturing and... encouraging entrepreneurship," he said.

"It means that we're rebuilding our infrastructure, our roads and our bridges, but also our high-speed rail lines and high-speed Internet access in places like rural Iowa, making sure that everybody who wants to reach a worldwide market is able to do so because they've got the connection to do it," said the US President.