Obama had a 51-44 percent edge over Romney in exit polling, and more Wisconsin voters said that the president would do a better job improving the economy and helping middle-class voters than his GOP rival would. A sizable 1 in 5, however, said they trust neither party's candidate on the economy, the main issue in the presidential campaign.
"These data points clearly demonstrate a very steep pathway for Mitt Romney to recover in the state," Obama's Wisconsin campaign director, Tripp Wellde, said in a statement.
But there are warning signs for Obama, too.
Independent voters, who made up a third of the recall electorate and typically decide close elections, broke for Walker 53-45. And the power was on display of both the GOP's robust national get-out-the-vote effort and of deep-pocketed Republican super political action committees, which poured $18 million into the state to help Walker. Unions, a key Democratic constituency, failed to get enough of their rank-and-file members to rally behind Barrett to give him a win, an ominous sign for a Democratic presidential candidate counting on those ground troops.
Four years ago, Obama won the state by 14 percentage points. Democrats John Kerry in 2004 and Al Gore in 2000 carried the state by less than a single percentage point. Observers say Tuesday's results may foreshadow a similar scenario in November.
Neither Obama nor Romney had run TV ads in the state though that likely will change, with campaigns and super PACs alike gearing up to pour money into Wisconsin.
Expect both candidates to visit more frequently, too. Obama and Romney had steered clear of the state in the heat of the recall campaign.
Careful not to weigh too deeply into what ended up being a losing race, Obama didn't campaign for Barrett, Milwaukee's mayor. Instead, the president posted his endorsement of Barrett on Twitter and emailed a Web video to Wisconsin supporters encouraging them to back Barrett. Obama also dispatched top surrogates including former President Bill Clinton and Democratic National Chairwoman Debbie Wasserman Schultz to the state.
Romney, for his part, has not visited Wisconsin, advertised here or had staff on the ground since winning the Republican presidential primary in April. Campaign officials said the former Massachusetts governor plans to convert the 26 offices that helped Walker into get-out-the-vote centers for his candidacy.
Romney hailed Walker's triumph as an endorsement of conservative fiscal policy, not a plug for the status quo, with national implications.
The results, he said in a statement, "will echo beyond the borders of Wisconsin."
While Obama has included Wisconsin in most of his scenarios for winning the White House, he conceivably could win a second term without it. But having to compete aggressively for Wisconsin means Obama will have fewer resources to spend in high-priority targets like Ohio and Florida.
"As both campaigns look at the data in the coming days and weeks, I think it's going to show that Wisconsin is a state that's a toss-up in the presidential campaign," said Romney's political director, Rich Beeson.
Democratic pollster Paul Maslin is betting that Walker's win will motivate Obama supporters from 2008.
"People aren't going to abandon their judgment," said Maslin, who is based in Madison and polled for Barrett's primary opponent Kathleen Falk. "That's why I think, at the end of the day, if it's really close, Obama wins."
Associated Press writers Steve Peoples in New Hampshire, Scott Bauer in Milwaukee and Ben Feller in Washington contributed to this report.
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