Opponents of Wisconsin Republican Gov. Scott Walker have submitted more than a million signatures seeking his recall in a statewide vote. The million-plus signatures amounts to nearly double the required number of 540,000 and is said to mark the largest recall effort in U.S. history. Walker is being challenged for pushing through a controversial law ending collective bargaining rights for most public workers. If the recall effort goes through, he would face a new election in late spring or early summer. Recall petitions were also submitted for Walker’s lieutenant governor, Rebecca Kleefisch, and four Republican state senators who helped pass the anti-union measure.