Obama told party activists in a live video teleconference that because of their support, the Iraq war ended, a major health care reform bill was signed into law and the military's "don't ask, don't tell" policy on gays ended.
"Because of you, because of all the memories I have of being in your living rooms, meeting you in a diner or seeing you over in a campaign office, I have never lost that same source of inspiration that drove me to embark on this journey in the first place," Obama told Democrats attending precinct caucuses.
Obama outlined his progress during the first term and asked party activists for their help as Republicans made their first step toward choosing a challenger among a field that included Mitt Romney, Rick Santorum, Ron Paul and others. Beyond its early voting status, Iowa was expected to be hotly contested in the fall election.
"We're battling millions of dollars of negative advertising and lobbyists and special interests who don't want to see the change that you worked so hard for to fully take root," Obama said. "And that's why time this time out is going to be, in some ways, more important than the first time out."
"The problems that we've been dealing with over the last three years, they didn't happen overnight and we're not going to fix them overnight," he said. "We've been making steady progress."
Obama wasted little time getting back in front of voters following a Hawaiian vacation spent largely out of the spotlight. On Wednesday, Obama will travel to Cleveland for an event focused on the economy.
The president used the video teleconference to talk directly with voters, an approach that encountered some audio problems during the short speech and question-and-answer session.
Obama was seeking to counter months of pounding by Republicans in Iowa and by the Republican National Committee, which has assailed Obama's economic record and tagged him as a president who has failed to live up to lofty expectations.
"Three years later, the president's promises of hope and change have been replaced with a record of failed leadership and policies that have made the economy worse," RNC spokeswoman Kirsten Kukowski said.
Iowa looks to be among about a dozen states that could shift either way in the 2012 campaign. Iowa has switched its support in each of the past three elections, supporting Obama in 2008, Republican President George W. Bush in 2004 and Democrat Al Gore in 2000.
In Des Moines, roughly 200 people gathered at a caucus site at Lincoln High School, making small talk and waiting for Obama to speak as a girls' basketball game was played in an adjoining gym. Several party loyalists said they thought Obama could reignite the loyal support he generated in 2008.
"No Republican candidate is exciting their base. There's just isn't anybody exciting their base, and if they can't get excited, I just can't believe they have a chance whatsoever," said Danny Waterman, 65, a retired police officer who supported Obama four years ago.
Rebecca Kaiser, 60, an insurance clerk who served as a precinct chairwoman for Obama's campaign in 2008, said the president's "hands have really been tied."
"Without the support of Congress he can't get anything done, and now it seems as though he's learning to put a little more pressure on them," Kaiser said. "I would have liked to have seen that earlier on, but hindsight is 20/20."
Trying to build on his 2008 win there, Obama's campaign has opened eight offices in the state and had held more than 1,200 training sessions, phone banks and other events and made more than 350,000 phone calls to supporters since April.
The president's re-election campaign emailed supporters a video of Obama's Iowa victory speech in January 2008, arguing he has kept the promises he made that night: making health care more affordable, cutting taxes for the middle class, ending the war in Iraq and reducing the nation's dependence on foreign oil.
Looking ahead, Obama faces more debate on extending payroll tax cuts, the same issue that consumed Washington during the final days of December.
Congress broke through a stalemate just days before Christmas, agreeing to extend the cuts for two months. Lawmakers will get back to work later this month to negotiate a full-year extension of the cuts, which Obama supports.
White House officials say the tax cut extension is the last "must-do" legislative item on Obama's agenda this year. His strategy for his fourth year in office will focus largely on taking executive actions that do not need approval from lawmakers as he seeks to break away from a deeply unpopular Congress.
Meredith reported from Des Moines, Iowa. Associated Press writers Julie Pace and Jim Kuhnhenn contributed to this report.