MADISON, Wis. (AP) -- Wisconsin election officials say Democrats have turned in enough valid signatures to force four Republican state senators into recall elections.

A memo Government Accountability Board staff released Friday concludes recall organizers have gathered thousands more valid signatures than they needed to force Senate Majority Leader Scott Fitzgerald and Sens. Van Wanggaard, Terry Moulton and Pam Galloway into elections.

The senators had challenged thousands of signatures, but after GAB staff reviewed the names they ultimately didn't find enough problem signatures to block the elections.

Democrats are trying to oust the senators and Republican Gov. Scott Walker and Republican Lt. Gov. Rebecca Kleefisch from office as revenge for passing a contentious law that stripped most public workers of nearly all their union rights.