"The change we seek is still months and miles away," Obama told a boisterous crowd in Houston in a speech in which he also pledged to end the war in Iraq in his first year in office.
"I opposed this war in 2002. I will bring this war to an end in 2009. It is time to bring our troops home," he declared.
In a race growing increasingly negative, Obama cut deeply into Clinton's political bedrock in Wisconsin, splitting the support of white women almost evenly with her. According to polling place interviews, he also ran well among working class voters in the blue collar battleground that was prelude to primaries in the larger industrial states of Ohio and Pennsylvania.
Clinton made no mention of her defeat, and showed no sign of surrender in an appearance in Youngstown, Ohio.
"Both Senator Obama and I would make history," the New York senator said. "But only one of us is ready on day one to be commander in chief, ready to manage our economy, and ready to defeat the Republicans. Only one of us has spent 35 years being a doer, a fighter and a champion for those who need a voice."
In a clear sign of their relative standing in the race, most cable television networks abruptly cut away from coverage of Clinton's rally when Obama began to speak in Texas.
Sen. John McCain of Arizona won the Republican primary with ease, dispatching former Arkansas Gov. Mike Huckabee and edging closer to the 1,191 delegates he needs to clinch the GOP nomination at the party convention in St. Paul, Minn. next summer. He also led in early returns from the Washington primary.
In scarcely veiled criticism of Obama, the Republican nominee-in-waiting said, "I will fight every moment of every day in this campaign to make sure that Americans are not deceived by an eloquent but empty call for change."
McCain's nomination has been assured since Super Tuesday three weeks ago, as first one, then another of his former rivals has dropped out and the party establishment has closed ranks behind him.
Not so in the Democratic race, where Obama and Clinton campaign seven days a week, he the strongest black presidential candidate in history, she bidding to become the first woman to sit in the White House.
Ohio and Texas vote next on March 4 - 370 convention delegates in all - and even some of Clinton's supporters concede she must win one, and possibly both, to remain competitive. Two smaller states, Vermont and Rhode Island, also have primaries that day.
With the votes counted in nearly three-quarters of Wisconsin's precincts, Obama was winning 57 percent of the vote to 42 percent for Clinton.
Wisconsin offered 74 national convention delegates. There were 20 delegates at stake in Hawaii, where Obama spent much of his youth.
The Illinois senator's victory left him with 1,303 delegates in The Associated Press' count, compared with 1,233 for Clinton. It takes 2,025 to win the nomination at the party's national convention in Denver.
Obama's victory came after a week in which Clinton and her aides tried to knock him off stride. They criticized him in television commercials and accused him of plagiarism for using words first uttered by Massachusetts Gov. Deval Patrick, a friend. He shrugged off the advertising volley, and said that while he should have given Patrick credit, the controversy didn't amount to much.
The voters seemed not to care.
Wisconsin independents cast about one-quarter of the ballots in the race between Obama and Clinton, and roughly 15 percent of the electorate were first-time voters, the survey at polling places said. Obama has run strongly among independents in earlier primaries, and among younger voters, and cited their support as evidence that he would make a stronger general election candidate in the fall.
Obama began the evening with eight straight primary and caucus victories, a remarkable run that has propelled him past Clinton in the overall delegate race and enabled him to chip away at her advantage among elected officials within the party who will have convention votes as superdelegates.
The economy and trade were key issues in the race, and seven in 10 voters said international trade has resulted in lost jobs in Wisconsin. Fewer than one in five said trade has created more jobs than it has lost.
The Democrats' focus on trade was certain to intensify, with primaries in Ohio in two weeks and in Pennsylvania on April 22.
Obama's campaign has already distributed mass mailings critical of Clinton on the issue in Ohio. "Bad trade deals like NAFTA hit Ohio harder than most states. Only Barack Obama consistently opposed NAFTA," it said.
Clinton's aides initially signaled she would virtually concede Wisconsin, and the former first lady spent less time in the state than Obama.
Even so, she ran a television ad that accused her rival of ducking a debate in the state and added that she had the only health care plan that would cover all Americans and the only economic plan to stop home foreclosures. "Maybe he'd prefer to give speeches than have to answer questions" the commercial said.
Obama countered with an ad of his own, saying his health care plan would cover more people.
Unlike the Democratic race, McCain was assured of the Republican nomination and concentrated on turning his primary campaign into a general election candidacy.
In one sign of progress in unifying the party, he split the conservative vote with Huckabee in Wisconsin.
Huckabee parried occasional suggestions - none of them by McCain - that he quit the race. In a move that was unorthodox if not unprecedented for a presidential contender, he left the country in recent days to make a paid speech in the Grand Cayman Islands.
McCain picked up endorsements in the days before the primary from former President George H.W. Bush and former Massachusetts Gov. Mitt Romney, a campaign dropout who urged his 280 delegates to swing behind the party's nominee-to-be.
