Wisconsin has been the source of considerable bad news for the Democratic Party of late, particularly for their union backers. First came the loss of the solidly pro-union Kathleen Falk to a more centrist opponent in the recent Democratic primary; now it appears that even this more moderate candidate is headed for a loss to Republican Scott Walker in June’s recall election.Yet Scott Walker’s poll numbers are not the main concern for Democrats. More troubling is a recent Marquette University poll which shows Mitt Romney and Barack Obama in a statistical dead heat in Wisconsin at 46 percent each. This is no small matter. As the Wall Street Journal points out, Wisconsin has been a reliably blue state for years. Republicans last won the state in 1984. In 2008, Obama won the state by more than 13 percent, nearly double his national average of 7 percent. If Wisconsin flips into the red column, it would be a major loss of a state generally assumed to be safe for the Democrats. Even if Obama eventually wins the state, a close race there could force the party to devote resources it would have preferred to spend elsewhere.This is only one, relatively minor poll, and it would be a mistake to read too much into it. Yet viewed in the light of Scott Walker’s recent successes in the state, it does appear that a significant shift is occurring. For decades, a strong Democratic coalition anchored by the unions made the Midwest one of the bluest regions in the country. But in Wisconsin at least the old coalition doesn’t seem to bring victory any more.If this continues, the Democrats are in trouble.