If independents supporting Mr. McCain believe he has wrapped up his party's nomination, they may cross party lines and support Mr. Obama in the Democratic primary, Mr. Burden said.
With similar demography and slumping manufacturing sectors, the Midwestern states mirror one another. Because Wisconsin is holding a primary rather than a caucus -- Mrs. Clinton has fared better in primaries -- Mr. Obama is trying to raise expectations for his opponent as she lowers them.
"By their own definition, Wisconsin would be a state you would think would be prime turf with them," Mr. Obama's campaign manager, David Plouffe, said.
Recent polls show Mr. Obama surging. The two latest polls in the state gave him leads of four and 11 percentage points. Since he arrived Tuesday, his rallies have drawn well. If he is able to win Wisconsin and his native state of Hawaii the same day, it would give him 10 straight victories heading into Ohio, where the latest poll showed Mrs. Clinton leading by 17 points.
Mrs. Clinton has tried to tamp down expectations in Wisconsin before key votes in Ohio and Texas next month. This week, Clinton strategist Mark Penn called Wisconsin "an uphill challenge." Campaigning this week, Mrs. Clinton has taken to calling herself "the underdog candidate." Nonsense, said Wisconsin Gov. Jim Doyle, who is backing Mr. Obama. Former President Bill Clinton, who campaigned in Wisconsin yesterday, twice won the state in presidential elections. "She is like an incumbent here," Mr. Doyle said.
The similarities between Ohio and Wisconsin are noteworthy. Both are swing states with populations that are whiter and a bit older than the nation as a whole. Each has an unemployment rate and union membership slightly above the national average. Each ranks near the bottom in prospective employment growth, according to a Moody's Economy.com index. Both are enduring population loss.
"Wisconsin is a little bit of a tell for Ohio," said Ken Goldstein, a professor of political science at the University of Wisconsin at Madison. "Either the Clinton campaign has done a brilliant job of managing expectations, or they're missing an opportunity here and they're in real trouble."
As the industrial Midwest grapples with globalization and the consequent economic insecurity, a study assessing progress among states into the "new economy" published last year by the Kauffman Foundation ranked Ohio 29th and Wisconsin 30th. Lead study author Robert D. Atkinson said, "They both tend to be less dynamic, and they have...similar kinds of economic anxieties."
That insecurity was playing to Mrs. Clinton's strengths a month ago, when she was drawing broad support among blue-collar workers. But after making inroads in Maryland and Virginia, Mr. Obama is trying to win support in Wisconsin's blue-collar community. On Wednesday at the General Motors Corp. plant in working-class Janesville, he told the crowd that if he becomes president, the government will be "there to support you and give you the assistance you need to retool and make this transition."
The Clinton campaign has countered with ads touting Mrs. Clinton's positions on health care and freezing home foreclosures and challenging Mr. Obama to a debate he hasn't accepted.
One difference between Ohio and Wisconsin voters could be attitudes toward the Iraq war, said Barry Burden, an Ohio native and professor of political science at the University of Wisconsin at Madison. "There's a greater hostility toward Bush in Wisconsin, his approval rating here is lower and the antiwar sentiment is stronger."
Mr. Obama has criticized Mrs. Clinton's record on the war, but the issue isn't a clean win for him, said Mr. Burden. Wisconsin's Madison-centric image as a liberal enclave is misleading when one looks at past elections, he said. Sen. John Kerry beat former Vermont Gov. Howard Dean here in 2004, and Michael Dukakis beat Jesse Jackson here in 1988.
Wisconsin has same-day voter registration that results in turnouts traditionally among the highest in the nation. That could bode well for Mr. Obama, who has fared well among independents. In the latest Republican polls, front-runner Sen. John McCain leads Arkansas Gov. Mike Huckabee by 20 percentage points.