Barack Obama has gained an 11th straight victory in the race for the Democratic presidential nomination by winning the Democrats Abroad primary.
He now faces his rival, New York Senator Hillary Clinton, in a TV debate in Texas ahead of crucial primaries there and in Ohio next month.
She is seeking to revive her campaign with wins in the two key states in order to stop Mr Obama's momentum.
Mrs Clinton now needs a majority of the remaining delegates to beat Mr Obama.
He has at least 1,351 - according to an Associated Press projection - of the 2,025 delegates he needs to secure the Democratic nomination at the party's convention in August.
'Yes we can' message
While Democrats Abroad, representing the party's supporters living in more than 30 countries, gives Mr Obama only 2.5 delegates over two for Mrs Clinton, it continues his winning streak.
Wisconsin's primary on Tuesday was significant for Mr Obama, says the BBC's Jonathan Beale, because he ate into Mrs Clinton's support base of white women and lower-income workers.
Correspondents say the blue-collar vote will be crucial in the Ohio and Texas contests, and the Clinton campaign has already begun targeting lower-income workers in its ads.
But in his drive to become the first black US president, Mr Obama has gained important support from some powerful unions, including the Teamsters and the Service Employees International Union.
The first-term Illinois senator has brushed off criticism from Mrs Clinton and Republican front-runner John McCain that he lacks substance.
His eloquent speeches and "yes we can" message of hope have inspired many voters.
"It's a choice between a politics that offers more of the same divisions and distractions that didn't work in South Carolina and didn't work in Wisconsin and will not work in Texas," he said to a crowd of 17,000 in Dallas.
"Or a politics of common sense, of common purpose, of shared sacrifice and shared prosperity."
Victories needed
But Mrs Clinton shot back at a New York fund-raiser, saying: "It's about picking a president who relies not just on words but on work, on hard work."
Mrs Clinton has pursued live debates with Mr Obama, hoping her keen grasp of policy issues will be seen to outweigh his sparkling rhetoric.
The Texas debate, at 0100 GMT Friday, is the first of two the Obama camp agreed to.
Many analysts are saying Mrs Clinton can only turn around her campaign with big victories in Texas and Ohio on 4 March.
She has not won a state primary or caucus since 5 February.
Her husband, former President Bill Clinton, said he thought she could win the nomination over Mr Obama if she won the two large states.
"If she wins in Texas and Ohio, she will win in Pennsylvania and I believe she will win the nomination," he said campaigning for his wife in Texas on Wednesday.
http://news.bbc.co.uk/1/hi/world/americas/7256937.stm