The primary for the special election in Arizona's 8th congressional district - the district formerly represented by Gabby Giffords - takes place today, with the special election to follow on June 12.
The Democratic field is already set. Ron Barber, the former district director for Giffords, is running unopposed. He has Giffords' endorsement.
On the Republican side, there are currently four candidates in the race: State Senator Frank Antenori; Martha McSally, a retired air force pilot; sports broadcaster Dave Sitton; and Jesse Kelly, a former marine who ran unsuccessfully against Giffords in 2010.
Kelly is seen as the favorite to win the nomination again this time around; polling has placed him in the lead. The National Republican Congressional Committee has remained neutral during the primary.
Barber, who was injured during the shooting on Jan. 8, 2011, has so far been a strong fundraiser - taking in over $500,000 through March 28, according to his FEC disclosures, far more than any of his Republican competitors. He has not yet begun to advertise on television.
Political spectators outside the state might be tempted to assume that because of his fundraising advantage, and because he has the endorsement of Giffords, Ron Barber will sail to victory on June 12. However, the eighth congressional district of Arizona tends to lean Republican. George W. Bush carried it in 2000 and 2004, and John McCain carried it in 2008.
Kelly has raised a little over $200,000 so far, and he mounted a strong fight against Giffords in 2010, losing the election by less than 2 percent. Giffords got 48.7 percent of the vote, Kelly taking 47.2 percent.
The race will likely be hard-fought, and Democrats and Republicans have begun painting their opponents as having political views which are too far left or right for the district.
"This seat has always been competitive and it remains competitive," writes Daniel Scarpinato, a spokesman for the National Republican Congressional Committee. "Southern Arizonans are looking for a check and a balance in Congress, but all Ron Barber is offering is to be a rubber stamp on President Obama's failed policies."
"Republicans are running to the extreme right in this primary, competing over who can be more supportive of out of touch policies that end Medicare and jeopardize Social Security" writes Jesse Ferguson, a spokesman for the Democratic Congressional Campaign Committee - the Democratic counterpart to the NRCC. "Arizona families want someone like Ron Barber who will fight to protect the middle class and seniors."
Turnout is expected to be low in the primary, and low in the general election, party officials say.
After the special election, the winner will not have very much time to acclimate to their new job in Washington, D.C. The seat will be up for grabs in the general election in November as well.