Leslie said she's moving into a smaller home no longer in the district where she was elected in 2010 because of reapportionment.
"I live in a big house. My daughter's gone now," Leslie said. "I bought a smaller home in December 2010. I thought I'd be able to move there."
But she lost that gamble, she said, when redistricting maps drawn by a panel of special court masters that put her new home in Brower's suburban and rural Senate District 15, which is evenly split in voter registration.
"I needed to make some personal decisions," Leslie said. "You have to live in your district 30 days before filing. The calendar forced my hand."
Candidate filing runs March 5-16.
"It's risky for me, yes. I could lose. But I could also win," Leslie said.
Brower described the surprise announcement a "partisan stunt" designed by Democrats to try to retain control of the upper chamber.
"A partisan move like this ... will be suspect in many people's minds," he said. "But that's fine. To me it's about the issues."
Brower said his campaign is well organized and he looks forward to the race.
"I think the contrast will be clear," he said. "I'm confident the people in my district, my neighbors ... share the same vision I share."
Democrats hold an 11-10 edge in the Senate, and Republicans are hoping to flip the advantage their way. Two southern Nevada incumbent Democrats, Shirley Breeden and Allison Copening, are not seeking re-election, and Republicans are hoping to claim those seats in November.
Leslie's resignation comes midway through her four-year term. She served six terms in the Assembly before winning election to the Senate in 2010.
Her district shuffle leaves her seat, now District 13, up for grabs. Democrats there have a sizeable voter registration advantage, and both Assemblyman David Bobzien, D-Reno, and Assemblywoman Debbie Smith, D-Sparks, are considering running.
"It's certainly an opportunity and I'm going to take a look at it," Bobzien said. "I'll be having conversations with Assemblywoman Smith as to how we move forward. Both of us would be strong candidates for that seat."
Brower served two terms in the Assembly until he was defeated in the 2003 primary by Sharron Angle, who also lives in the district. Angle, a tea party conservative, was the 2010 Republican nominee in Nevada's U.S. Senate race and lost to the Democratic majority leader, Harry Reid.
A former U.S. attorney, Brower returned to politics last year when he was appointed by the Washoe County Commission to fill the District 15 seat following the retirement of longtime Republican Sen. Bill Raggio.
Brower was also a candidate for Nevada's open U.S. House seat last year before the state Republican Party endorsed Mark Amodei, who won a special election against Democratic Kate Marshall.