Instead, in Wisconsin, Obama won big among independent swing voters, who might hold the key to the fall election. Independents and Republicans cast more than one-third of the Democratic vote, and Obama carried them by a 2-to-1 margin, according to an Election Day survey of voters as they left polling places.
His crossover appeal could be a pivotal factor in the next primaries, in Ohio and Texas, which allow independents to participate. Ohio, with its large, white, working-class electorate, has emerged as a must-win for Clinton.
As he did last week in Maryland, Obama won an increasing share of white working-class voters, running even with Clinton among those who earn $15,000 to $30,000 a year and those without a college education. He also ran almost even with her among Catholics, who cast about two in five votes.
An overwhelming majority of Wisconsin's Democratic voters took a sharply negative view of the North American Free Trade Agreement from the Bill Clinton years. About seven in 10 said it had cost the country jobs, and Obama won most of their votes.
Obama has sought to tie NAFTA to Hillary Clinton, who initially supported it but more recently has criticized the way it was enforced, and called for a "timeout" on future trade deals.
Clinton's campaign has argued that her victories have come in states that a Democrat would need to carry in November, while many of Obama's have come in heavily Republican states.
However, Wisconsin figures to be a major battleground in the general election. It has been almost dead even in the past two presidential elections, going Democratic by an eyelash both times.
The tone of the Democratic race turned sharply negative last week, after Clinton launched attacks on Obama over issues such as Social Security and his refusal to debate her in Wisconsin.
Clinton aides have accused Obama of plagiarism, for using identical phrases in speeches that Deval Patrick, the first black governor of Massachusetts, used in his.
Obama has fought back, with response ads in Wisconsin and attacks of his own at campaign events. Yesterday, during his first stop in Texas, he criticized Clinton's plan for a five-year interest-rate freeze on adjustable-rate mortgages, warning that it could deepen the subprime lending crisis.
"Even more families could face foreclosure," he said in San Antonio. "That's why one economic analyst called her plan disastrous."
