Mason, a Democrat, made the announcement on the eve of the 20th anniversary of his first election victory — Nov. 7, 2006, when he won a state Assembly seat representing Racine. He left the Assembly in 2017 after winning a special election to succeed Mayor John Dickert, who departed mid-term for another job. Mason then secured full four-year terms in 2019 and 2023.

"After 20 years, it's time to pass the torch of leadership to the next generation," Mason said in an interview.

He will remain in office until his current term ends in April. The decision, he said, was made recently with his family. Mason and his wife, Rebecca, a Racine estate planning and elder law attorney, have three children in high school.

"It's important to have work-life balance, and I'm looking forward to the next chapter where I can have a little bit more of that moving forward," he said.

Mason's departure coincides with a historic shift in state government: Democrats will hold the governor's mansion and both chambers of the Legislature for the first time since Republicans swept all three in 2010. That unified control could revive policies Democrats have long championed, including increased shared revenue for cities like Racine.

The new political landscape contrasts sharply with most of Mason's tenure in the Assembly, which was dominated by the fight over Act 10 — the law introduced by then-Gov. Scott Walker that stripped most collective bargaining rights from public employees except police and firefighters.

Reflecting on his time as mayor, Mason pointed to nearly 20 accomplishments, foremost among them the completion of a community center and health clinic serving a northwest side district. That same area is also the site of a major affordable housing project. He also cited a city internship program for young people, a jobs initiative connecting workers with construction trades, and reductions in gun violence.

One longer-term project remains unfinished, and Mason hopes his successor will carry it forward: establishing commuter rail service linking Milwaukee with Racine, Kenosha, and other cities to the south. Federal funds would provide the bulk of financing, but the process is slow-moving. Two decades ago, a similar rail effort in the corridor collapsed when Republican state lawmakers balked at the plan.

"You need a muscular and robust partnership with the Wisconsin Department of Transportation to make a project to this scale go forward," Mason said. He expressed enthusiasm about Gov. David Crowley's openness to improved public transportation and "having a Legislature that cares deeply about it."

Mason also noted that Trevor Jung, who won his state Senate race on Tuesday and currently serves as Racine's transit director, shares his passion for the rail project. "I'm really excited for him to advocate for this up in Madison," Mason said.

Mason did not rule out a return to politics but declined to speculate on specific races in the next four years. Asked whether he might join the incoming Crowley administration, he said, "I don't have anything definitive lined up, but I've not ruled anything out either."

He did, however, draw one clear line: "I did rule that out as the next thing that I would do," he said of becoming a lobbyist. "But that notwithstanding, you know I'm excited to figure out what the next chapter of my life looks like."