Wisconsin Gov. Scott Walker (R) is fighting for his political life in Tuesday’s recall election in the Badger State.

But what’s up with the recall? And how does it work?

We explained it all last year when several Republican state senators faced similar recalls. Here’s an updated version for the Walker race:

Spectators applaud at a rally held by the Racine Tea Party PAC in Gorney Park in Caledonia, near Racine, Wis., Saturday June 2, 2012. The rally was held in advance of Tuesday's recall election in which Democratic opponents are running against incumbent Gov. Scott Walker, Lt. Gov. Rebecca Kleefisch, and State Sen. Van Wanggaard of Racine. (Mark Hertzberg/Associated Press)

* What is a recall?

A recall is a means of removing a public official from office in the middle of his or her term — usually because he or she has done something that is, in the eyes of opponents, beyond the pale.

In order to begin the process, though, those opponents must gather a very large number of signatures, meaning it’s generally only an option that is used under extreme circumstances.

* Why is this happening?

In the 2010 election, Republicans swept Wisconsin state government, assuming the governorship and both houses of the legislature. Republicans in the legislature, in conjunction with Walker, soon put forward an austerity budget that ended collective bargaining for public employees.

Democrats fled the state to prevent the state Senate from having enough members present to vote on the budget. Thousands of protesters gathered at the state capitol in opposition to the law. After weeks of stalemate, Republicans separated the union provision from the rest of the budget, allowing them to vote on it without Democrats present.

Walker signed the measure into law, provoking an immediate backlash. Democrats began gathering signatures on recall petitions against all eight eligible Republican state senators, and Republicans responded by attempting to recall all eight eligible Democratic state senators, arguing that they shirked their duties by fleeing the state.

In the end, two GOP state senators lost their seats, but Republicans maintained a narrow majority.

Walker couldn’t immediately be recalled (see below), but Democrats quickly turned their efforts to recalling him as well, resulting in Tuesday’s contest.

* Who is eligible for recall?

In Wisconsin, any elected state official who is more than a year into his or her term can be recalled. That requirement is why Walker, about half the state Senate, and all of the House were not vulnerable to recall last year.

Once the threshold passed for Walker, though, Democrats successfully gathered more than one million signatures to initiate his recall.

* How rare are recalls?

Recalls are very rare — especially successful ones — and only 19 states even permit them.

The last governor who was successfully recalled was California’s Gray Davis (D) in 2003, when Arnold Schwarzenegger (R) succeeded him. Before him, the only previous example was North Dakota’s Lynn Frazier in 1921.

In Wisconsin, only four state senators (including the two last year) have been recalled in the state’s history.

Only three times in American history has a recall election switched party control of a legislative chamber: In Michigan in 1983, Wisconsin in 1996 and California in 1995.

* Why does it matter?

The race is seen as a referendum on tough austerity measures in a swing state and, perhaps more importantly, labor’s third crack at sending a message in Wisconsin.

Democrats and unions already failed to win a key state Supreme Court race in early 2011 and came up shy of re-taking the state Senate later that year. Walker is the third try — and potentially the third strike. Whatever happens in the Badger State will bolster one side in the debate over where the public really stands on economic policy and union rights.

Liberals discouraged by the 2010 elections and the rise of the tea party hope these fights will spark more enthusiasm going into 2012. Conservatives want to prove that, in spite of high-profile protests, they have the winning argument and the true grassroots energy.

National groups on both sides have poured money and volunteers into the state, with nearly $100 million spent between last year’s recalls and the Walker race.

Recall elections are on the rise nationally, and these high-profile races will likely only accelerate that trend.