Obama traveled across Wisconsin during the day, hoping to add the state to an impressive string of primary victories. At the same time, he hoped his second labor endorsement in as many days, would help him in Ohio, Texas and other primary states, and block Clinton's efforts to establish a campaign firewall.
The Illinois senator won the endorsement of the 1.9 million-member Service Employees International Union, one day after he collected the support of the United Food and Commercial Workers, a politically active union 69,000 members in Ohio and another 26,000 in Texas. The food workers also have 19,000 members in Wisconsin, which holds a primary Tuesday.
Addressing voters in Wisconsin, Obama accused Clinton of lashing out at him as a cheap ploy to get ahead and being so divisive that she couldn't pass her signature effort of health care reform.
"Hollering at Republicans and engaging in petty partisan politics didn't help health care get done," he said. "The American people don't want to play the same games. They don't want the cheap shots. They don't want the negative ads. What they are looking for are solutions and bringing people together."
Obama's advisers say even though some of his supporters assume she is on the verge of collapse, it would be a mistake to underestimate the Clintons. They have proven their ability again and again to make a comeback when they were at their lowest.
Clinton has suffered a spate of crippling developments - eight straight losses, campaign finance problems, a shake-up of her staff - but has fresh reason for hope in recent polls. A poll of Wisconsin voters released Friday found Obama with only a slight edge in a state he was expected to win.
In Wisconsin, she's airing ads criticizing Obama for refusing to debate her in the state - which Obama called a "curious argument" since they have two debates scheduled in the next two weeks. But he added more campaign stops before Tuesday's primary to shore up his support.
Recent polls in Ohio and Pennsylvania show Clinton with a more than 15-percentage point advantage. She's pinning her campaign hopes on winning Texas and Ohio on March 4 and Pennsylvania on April 22.
Obama's support from SEIU and the 1.3-million member United Food and Commercial Workers a day earlier gives him an organizational boost in those critical states with large numbers of working-class voters. Sarah Swisher, a superdelegate and an SEIU member from Iowa City, switched from Clinton to Obama after her union's endorsement.
In the latest delegate count by The Associated Press, Obama had 1,280 and Clinton 1,218/ Obama has cultivated an image of being above the fray, and his criticism of Clinton usually comes in the form of a response to her charges. But he's not above upping the ante, as he did Friday during a stop in Milwaukee.
During a news conference, he was asked about Clinton's accusation that he watered down a bill regulating the nuclear industry. He pointed out that Clinton is criticizing him for a bill she voted for and touted on her Web site.
"I understand that Senator Clinton, periodically when she's feeling down, launches attacks as a way of trying to boost her appeal," he told reporters.
At a subsequent rally at the downtown Midwest Airlines Center, Obama brought up her latest criticism of him as someone who gives a good speech but doesn't have much action to show for it. Clinton told voters in Cincinnati Friday, "This primary election offers a very big choice to the voters of Ohio. You can choose speeches or solutions."
"She's right," Obama said in Milwaukee. "Speeches alone don't do anything. But you know what, neither do negative attacks."
