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Voters in southeastern Arizona will participate in a special election to fill a vacant House seat on Tuesday night. Gabrielle Giffords (D-Ariz.) stepped down from her congressional position in January to focus on her recovery from a gunshot wound she sustained a year earlier during an assassination attempt.

Democrat Ron Barber, a former aide to Giffords who was also injured in the shooting, will run against Republican Jesse Kelly, 30, a former marine with Tea Party roots who lost narrowly to Giffords in 2010. The winner will serve the remaining six months of Giffords’ term.

Arizona’s 8th district is Republican-leaning, but the race is close as this is a swing district: Giffords won only by a 4,000 margin in 2010 against Kelly. In a poll released Monday, 53% of voters chose Barber compared to 41% who chose Kelly. Still, experts say the margin is too close to project for certain.

In preparation for tonight's vote, here are a few things to know about Giffords and the Arizona election:

1) Giffords is important

The former congresswoman is in the minds of Arizonans who are very consciously voting for “Gabby’s seat.” They love their former congresswoman, who has endorsed Barber -- a sympathetic figure also injured in the shooting. The unique events surrounding the election have made for a more civil campaign that has toned down partisan punches.

2) Giffords is not not everything

Giffords influences general sentiment and sympathy for Barber, but the race is still close and focused on more than just Giffords. The public likely sees the assassination attempt as an incidental tragedy rather than indicative of a systemic problem. Indeed, neither candidate has focused on the shooting in their campaigns. National politicians who had vowed to address gun control have failed to make any reforms.

3) It’s the economy 

While immigration dominated the close election in 2010, the economy and job creation tops this year’s agenda for voters. Kelly would institute lower taxes and more energy production to improve the economy. He would also reduce federal regulations and environmental protections to spur oil and gas drilling. Barber has spoken about growing the solar industry and cutting taxes for the middle class only; he wants the wealthy to “pay their fair share.”

4) Immigration still matters

Immigration is still a controversial issue in the district. Kelly has vowed to build a double-layer fence along the district's border with Mexico. Barber doubts that the fence would be effective, but rather calls for more manpower, horse patrols, and drones.

5) For Democrats, a Barber win would validate their campaign strategy 

Democrats have called attention to GOP runner Jesse Kelly’s past statements about overhauling Medicare and Social Security. Early and frequently in the campaign, the Democrats released clips of Kelly criticizing the programs and desiring their overhaul. In a region with a growing population of retirees, focusing on social services and using Kelly’s own statements against him worked in 2010 for Giffords and seems to be working now.

6) For Republicans, a Kelly win would be a referendum on the Democrats

The GOP strategy has been to link Barber to the national Democratic image; namely Obama, and House minority leader Nancy Pelosi (D-Calif.) on issues such as health care policy and the economy. Barber has tried to distance himself from the national leaders, but a Republican win would signal voters’ frustration with the president and national policy.

7) Whatever happens, it won't decide the House majority 

Outside sources have funded up to $2 million of the campaign in hopes of influencing the House majority. Republicans now hold a 240-192 advantage with three vacancies, including Giffords' seat. A Democrat lost would make it harder to win the 25 seats needed for a blue majority. But one election, especially an unusual case such as tonight’s, cannot be a litmus test for every other state.