"You have put us within reach of the Democratic nomination," Obama told cheering supporters in Des Moines, addressing a majority white crowd that helped launch his improbable path toward the nomination more than four months ago.
Speaking before the Oregon primary results were announced, Obama continued to focus on his campaign for "change," using the word at least 15 times during his address.
"You came out on a cold night in January," he told the Iowans gathered on the capitol grounds in Des Moines. "You stood for change, and because you did, a few more stood up, and then a few thousand stood up and then a few million."
With half of the Oregon vote results in, Obama led Sen. Hillary Clinton by 16 points in the night's slightly bigger contest. He was projected to win at least 18 of that state's 52 delegates to 10 for Clinton.
In Oregon, a majority of voters called themselves liberal, according to a phone poll conducted for the Associated Press. Nearly six in 10 whites there backed Obama. The Illinois senator and Clinton were evenly dividing working-class whites -- those who have not finished college -- a group that has decisively stuck with Clinton in most states this year.
In addition, only about one in 10 voters in Oregon said the race of the candidates was important, one of the lowest proportions in any primary state this year. They were evenly divided between the two Democrats, but heavily backed Obama when he was pitted against Sen. John McCain.
In an e-mail to supporters late Tuesday, the Obama campaign asserted that it had secured "an absolute majority of all the delegates chosen by the people in this Democratic primary process."
But during his speech in Iowa, Obama sought to reach out to Clinton, heaping praise upon rival Clinton and taking aim at presumptive GOP nominee McCain of a campaign run by lobbyists.
"You are Democrats who are tired of being divided, Republicans who no longer recognize the party that runs Washington, independents who are hungry for change," he said, speaking to a crowd at the Iowa Capitol.
Obama said the night's contests gave him a majority of the delegates elected in the 56 primaries and caucuses combined. That is distinctively separate from the nearly 800 super delegates who hold the balance of power at the Democratic convention and will ultimately decide the party's nominee.
"We still have work to do to in the remaining states, where we will compete for every delegate available," he said in an e-mail sent to supporters. "But tonight, I want to thank you for everything you have done to take us this far -- farther than anyone predicted, expected or even believed possible."
The night also brought more good news for the Obama fundraising team. The campaign reported more than $37 million in the bank for his presidential run at the start of May, the AP reported. Obama raised more than $31 million from nearly 1.5 million donors for the primary race in April, a substantial sum but smaller than previous monthly totals. Clinton's campaign announced it had also raised $22 million in April, representing the campaign's second best fundraising month to date.
On the Republican side, McCain had $22 million on hand for the fall campaign at the start of May and raised nearly $18 million in April, his best month yet, but still third among the candidates.
In a sign of confidence on the front-runner's part, party officials said discussions were under way to send Paul Tewes, a top Obama campaign aide, to the Democratic National Committee to oversee operations for the fall campaign.
In another sign that the race may be nearing an end, Clinton and Obama praised one another and pledged a united party for the general election -- a distinctively more pleasant tone than the sometimes cantankerous barbs that were traded before the Pennsylvania primary.
"I commend Senator Obama and his supporters and while we continue to go toe-to-toe for this nomination, we do see eye-to-eye when it comes to uniting our party to elect a Democratic president in the fall," Clinton told supporters in Louisville, Ky.
Obama sought to make the bruising primary an asset as the party looks to the fall.
"Now some may see the millions upon millions of votes cast for each of us as evidence that our party is divided," Obama said. "I see it as evidence that we have never been more united in efforts to take this country in a new direction."
In addition to appealing to party unity, Obama sought to flesh out his policy vision as he builds on his continued theme of "change".
The Ill. senator spoke of health insurance for every American, better educational opportunities and "an energy policy that doesn't rely on buddying up to the Saudi Royal Family and then begging them for oil."
The Democrats' state-by-state contests end June 3 with contests in Montana and South Dakota.