Former Arizona Democratic Party Chairman Don Bivens formally announced his Senate campaign this morning in a video posted to his campaign website.
"I'm not a politician. I've spent my entire career in the private sector working with business large and small," Bivens, a partner at Snell & Wilmer, said in the video. "I'm running for the United States Senate because we can't keep sending the same folks back to Washington and expect a different result."
Bivens is the first Democrat to officially enter the race, which Roll Call Politics rates as a Tossup.
Giffords was a likely Senate candidate until she was shot in the head in January, and she's expected to run for re-election if she seeks any office next year.
Rep. Jeff Flake is the frontrunner for the Republican nomination, though he'll have some competition from wealthy business investor Wil Cardon and a couple of others.
GOP Sen. Jon Kyl's retirement made Arizona one of only a handful of possible pickup opportunities for Democrats, including Nevada and Massachusetts, in a year when the party is defending more than twice as many seats as Republicans. The GOP must win four seats to reclaim the Senate majority.