Rep. Gabrielle Giffords' decision to step down from her congressional seat sets up a wide-open race to fill her spot in a conservative-leaning Arizona district that has a history of electing moderates from both parties.

The congresswoman's decision announced Sunday also will trigger not one but two entire election cycles before the end of the year, with different district lines in each thanks to congressional redistricting.

Gov. Jan Brewer will call a special primary election for some time in April and then a general election in June to fill Gifford's seat in the 8th Congressional District in southeast Arizona. That will be followed by a regular primary in August and the November general election for the renumbered 2nd District that covers most of her current territory.

Brewer, a Republican, doesn't have any leeway on when or whether to hold the special election, and said Sunday that politics will not play a role in her selection of a date.

"I want to make it perfectly clear that all these time lines and the way that it goes and the way that it's happening and the procedures are all in statures," she said. "So we're going to follow those to the line."

Giffords would have been heavily favored to win reelection after gaining immense public support as she recovered from a shooting at a Tucson meeting with constituents last year.

The popular three-term Democrat's recovery from a gunshot wound to the head was described as just short of miraculous, but in the end she decided she couldn't run again.

A bevy of Republicans and Democrats have been mentioned as possible candidates, with several in the GOP already having official exploratory committees.

Giffords won her three terms by championing border security and defense, and her predecessor, Republican Jim Kolbe, was a moderate Republican who drew enough Democratic voter support to win 11 terms before retiring in 2006.

Giffords barely squeaked out a victory just two months before she was shot, winning by only about 1 percent over a tea party Republican.

Brewer acknowledged Sunday that the twin election cycles were going to create a mess, especially for potential candidates, but the law requires her to call the special election.

"I think that it's putting a lot of pressure on a lot of people awfully quick, given the fact that they're going to be filling that continuing seat that expires this year, and then we have elections coming (along) new congressional lines," Brewer said. "So there's going to be a lot of confusion in that congressional district.

Even quirkier, the deadline to turn in nominating signatures for the general election cycle comes before the special general election.

Republican who have expressed interest in the seat include state Sen. Frank Antenori and sports broadcaster Dave Sitton, among others. Several Democratic state lawmakers are mentioned as possible candidates, and the name of Giffords' husband, astronaut Mark Kelly's, has been bandied about, although he's publically quashed such speculation.

"That's the great `mentioner' out there, and there are going to be a lot of people mentioned," said Arizona Democratic Party chairman Andrei Cherny. "I think the best rule in situations like this is `the folks who are talking don't know and the folks who know aren't talking.'"

"I'm sure both parties and candidates of all stripes will in the days to come be thinking wide and hard about this district, and I'm sure there's going to be a very vigorous contest," Arizona Democratic Party chairman Andrei Cherny said Sunday. "But today's about thinking about a member of Congress who's going to be irreplaceable no matter who wins that seat."