Democrat Barack Obama has easily beaten Hillary Clinton in Wisconsin and Hawaii, extending his US presidential winning streak and putting pressure on his rival to win next month in Ohio and Texas to salvage her campaign.
Mr Obama has now scored ten straight victories in Democratic nominating contests.
Republican presidential candidate Senator John McCain celebrates his Wisconsin win at a rally in Columbus, Ohio
Both Democratic candidates looked ahead to March 4th showdowns in two of the biggest states, Texas and Ohio, which have a rich lode of 334 convention delegates at stake and where Mrs Clinton desperately needs to win.
"The change we seek is still months and miles away, and we need the good people of Texas to help get us there," Mr Obama said at a rally in Houston after noting his win in Wisconsin.
Up for grabs in Wisconsin and Hawaii were a combined 94 delegates to the August convention that selects the Democratic presidential nominee in November's election. Mr Obama has a slight lead in pledged delegates won in state presidential contests.
Republican front-runner John McCain also won in Wisconsin, and then later in Washington state, taking another big step toward becoming his party's nominee in the presidential election.
Mr McCain, an Arizona senator, beat his last remaining major rival, former Arkansas Governor Mike Huckabee, to expand his huge and practically unassailable lead in delegates.
"Thank you Wisconsin for bringing us to the point where even a superstitious naval aviator can claim with confidence and humility that I will be our party's nominee for president," Mr McCain, a former Navy fighter pilot and Vietnam prisoner of war, told supporters in Columbus, Ohio.
Mr McCain made clear who he thought would win the Democratic race, taking direct aim at Mr Obama in a preview of a possible general election match-up.
Senator Hillary Clinton at a rally in Ohio
"Will we risk the confused leadership of an inexperienced candidate?" Mr McCain asked. "I will fight every moment of every day in this campaign to make sure Americans are not deceived by an eloquent but empty call for change that promises no more than a holiday from history," he said.
Mr Obama took his own shot at Mr McCain, noting his support for President George W. Bush's economic policies and his support for a prolonged US military presence in Iraq. "He represents the policies of yesterday and we want to the be the party of tomorrow," the Illinois senator said.
Mr Obama's win in Wisconsin was particularly meaningful, coming in a general election swing state with a large population of blue-collar workers - a big part of Mrs Clinton's constituency and a similar demographic to Ohio.
Mr Obama now has 1,156 pledged delegates to Mrs Clinton's 1,014, according to a count by MSNBC. A total of 2,025 are needed to win the nomination.
Mrs Clinton, a New York senator and former first lady, is the early favourite in both Texas and Ohio, although one public opinion poll in Texas on Monday showed the race in a statistical dead heat.
Mrs Clinton did not mention the Wisconsin results during a rally in Youngstown, Ohio, after the race was called. "We can't just have speeches. We've got to have solutions," she said. "While words matter, the best words in the world aren't enough unless you match them with action."