By all estimates, the Wisconsin recall election—only the third in the nation’s history—is going to be a close vote. As a result, mistakes can have grave consequences for those seeking to replace the controversial Walker who has, in his short time in office, ended many collective bargaining rights for state employees, made huge cuts in the state’s education and health care budgets, and, according to many, taken steps to dramatically curtail voting rights for Wisconsinites more likely to vote for Democrats.

Officials with Minnesota’s largest public employee union say they have received several threatening phone calls and e-mails in response to their recent “tax the rich” ad campaign.