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Madison - Tuesday brings a series of recall elections unprecedented in the history of the state or nation.

Since 1908, there have been 20 recorded state legislative recall elections held in the United States, according to one recall expert. Wisconsin is in the process of holding nine such elections in the space of a month.

With control of the Wisconsin Senate in the balance, six Republican state senators will face a recall vote Tuesday. One Democratic senator has already weathered a recall attempt, and on Aug. 16, two more Democrats will be up for recall.

"Wisconsin has taken a quantum leap in a fast-changing process, in what has been a growing use of the recall" nationally, said Joshua Spivak, who writes the Recall Elections Blog .

There is intense interest - from voters on the street to national political groups - in the elections sparked by lawmakers' positions on GOP Gov. Scott Walker's law ending most union bargaining for most public workers.

Tens of millions of dollars are being spent on the recall campaigns by candidates and independent groups. President Barack Obama's Organizing for America was pulling together canvassing drives Monday, and the Tea Party Express was concluding a bus tour of the state with rallies in Rhinelander and De Pere.

State Government Accountability Board officials are not releasing turnout projections because of the unusual, difficult-to-predict nature of the election. But people on both sides of the races were predicting healthy turnouts.

Fond du Lac City Clerk Sue Strands estimated an exceedingly high turnout Tuesday of 75% to 80% of registered voters in her area, where Sen. Randy Hopper (R-Empire) faces a challenge from Democrat and former Oshkosh Deputy Mayor Jessica King. Strands said the volume of calls, voter registrations and absentee ballot requests that her office has been receiving is comparable to those in a gubernatorial race.

Portage City Clerk Marie Moe would not give a turnout estimate, but she said her office has given out roughly the same proportion of absentee ballots as in November's gubernatorial election.

Joe Heim, a political-science professor at the University of Wisconsin-La Crosse, said Democratic and Republican voters have gotten more engaged as a result of the state's political climate.

"It's extremely historical and unprecedented," Heim said. "(Republicans) woke up a sleeping giant and energized a group of people that had not been . . . particularly active in politics in recent years."

Uncharted territory

John Hogan, who is managing Senate Republicans' recall efforts, acknowledged the national implications of the elections and said voters would support GOP senators for helping to cope with the state's budget problems.

"The nation is watching. What you have here is a state making a decision on which way do you go," Hogan said. "We need legislators to make the tough decisions."

Wisconsin Democrats said the elections were a reaction to a divisive plan by Walker that he never campaigned on last year and they had hopes of taking enough seats to win back the Senate.

"We all know we're operating in uncharted territory here, completely unprecedented. It's an incredible thing to be a part of," said Mike Tate, chairman of the state Democratic Party.

Republicans control all of state government including the Senate, where they have a 19-14 advantage. That means Democrats would need to win at least three seats Tuesday to take back the Senate.

But if the Democrats took back the Senate by just three or four seats, the two recall elections for Democrats the following week would give Republicans a chance to flip that house yet again.

Scholars interviewed by the Journal Sentinel in the spring could cite only three times in American history when more than one state legislator had been recalled at roughly the same time over the same issue: two in Idaho in 1971 over a pay raise, two in Michigan in 1983 over a tax vote and two Republicans in California months apart in 1995 over their collaboration with Democrats.

Only two state legislators have been successfully recalled in Wisconsin history.

Spivak, a senior fellow at the Hugh L. Carey Institute for Government Reform at Wagner College in New York, said he believes recalls are increasing at the national level in part because of technologies such as computer databases, spreadsheets, blogs and social media that make it easier to track and communicate with voters who would be interested in signing recall petitions and volunteering for and donating money to recall efforts. Another recent factor is the difficult economic times facing both the state and nation.

Spivak said Wisconsin was a natural place for a recall to happen because it is a state where control of government regularly switches from one political party to another, raising the stakes for a recall effort and making it more attractive.

"Wisconsin's a real battleground state," Spivak said. "It makes sense that it would happen in a state that has the possibility of going either way."

Though some have argued that having recall elections will have a chilling effect on state lawmakers facing potentially unpopular decisions in the future, Heim disagreed.

"This is almost a version of a perfect storm. . . . There's just few issues that can create that kind of intensity," Heim said.

IDs not yet required

In addition to the recall races, Tuesday's election is another day on which the state's new voter ID law gets its "soft implementation."

As they did in the July 12 and 19 elections, poll workers will be asking voters for a photo ID, but people will be allowed to vote even if they don't have one. If they don't, they'll receive written information about the new law. The IDs will be required in elections starting next February.

Already required now, though: Voters must sign the poll list and won't be allowed to vote unless they do. Exceptions will be made for voters who can't physically sign their names.

Also in effect for this election are new rules requiring anybody who registers at the polls to have lived in the district for 28 days; the previous period was 10 days.

Meanwhile, Glendale reported confusion among some voters about where to vote Tuesday. The confusion was apparently caused by a letter sent out by We Are Wisconsin, a labor group backing Democrats in the recalls.

The letter, signed by U.S. Sen. Herb Kohl, a Democrat, included instructions telling at least some voters their polling place was at Glendale's City Hall. That was Glendale's only polling place for a July 12 primary election, but voters Tuesday will vote at their usual polling places, said Susanne Hanaman, city clerk-treasurer.

One Glendale resident reported that We Are Wisconsin called over the weekend to point out the error and correct it.

Emma Roller of the Journal Sentinel staff contributed to this article.