In a potentially ominous sign for the Obama campaign, a new poll has declared Wisconsin a true tossup state, finding President Barack Obama and Mitt Romney locked in a 46-46 tie among likely voters.

As the Obama team eyes potential paths to victory in November, all count on the president winning the reliably blue states of New England, the Midwest and the Upper Midwest, all of which went for Al Gore in 2000 and John Kerry in 2004. A loss of any of the bigger traditionally blue states—particularly Pennsylvania, Michigan or Wisconsin—would scramble the Obama math and make matters much easier for Mr. Romney, allowing him to lose in Virginia or Ohio without that automatically jeopardizing his chances.

Mr. Obama won Wisconsin handily in 2008, and has lead there by wide margin