The list of potential Republican candidates who could jump into the race for retiring Sen. Jon Kyl's (R-Ariz.) seat starts at close to 10 candidates, with GOP insiders pegging Rep. Jeff Flake (Ariz.) the early front-runner. 

Flake is likely to jump into the race quickly, according to a GOP source — an early entry that could help thin the Republican field.  

Other possible contenders include Rep. Trent Franks (Ariz.) and former Reps. J.D. Hayworth (Ariz.) and John Shadegg (Ariz.). Hayworth told The Hill on Thursday that he's weighing a run; Shadegg wouldn't say whether he's likewise mulling a bid, but did urge Kyl to reconsider his decision to retire. 

Other potential candidates, according to Republicans: Maricopa County Sheriff Joe Arpaio, former state Treasurer Dean Martin and state Senate President Russell Pearce. 

Former Gov. Fife Symington also expressed interest Thursday. Symington even floated former Arizona Cardinals quarterback Kurt Warner as a potential candidate for the seat to Politico

One high-profile Republican who has already taken herself out of the running for the Senate seat is Gov. Jan Brewer, a star among conservative activists thanks to her championing of the state's tough anti-illegal immigration law. 

On the Democratic side, the field of potentials is led by former Arizona Gov. and current Homeland Security Secretary Janet Napolitano. 

Rep. Gabrielle Giffords (D-Ariz.) was seriously considering a run for Kyl's seat before last month's shooting in Arizona. Giffords had told staff that she intended to make a bid for the seat should Kyl opt for retirement. 

Giffords is recuperating from a gunshot wound to the head, and it won't be known for some time if she will fully recover from the injury. She is, however, widely considered the Democrats' ideal candidate for the seat. 

Other Democratic possibilities include Rep. Ed Pastor (Ariz.), U.S. Attorney Dennis Burke and former Rep. Ann Kirkpatrick (Ariz.).