"Like many of my friends and neighbors, I'm frustrated right now that Washington is not listening, and it's not delivering for the middle class," said Callis, who left the bench on Friday so she could run for the seat. "As Chief Judge, I've delivered reforms when Washington didn't, and I'm running to deliver solutions for middle class families who are looking for good-paying jobs, and someone to protect Medicare and Social Security."

Davis is a top Democratic target this election cycle and barely won a swing district in 2012 against a weak Democratic opponent. But he's been off to a quick fundraising start, bringing in $390,000 in the first three months of 2012.

Davis's 2012 opponent David Gill had been considering mounting yet another bid for the seat. But he instead took a job with the state, clearing the way for Callis.