He appeals to a broad swath of constituents  rural, Latino, politically centrist  and has served as both friend and foe to the governor, a fellow Republican, and as the sole person Democrats have found they can turn to when they need one Republican vote on policy and budget issues. Budget bills in California require two-thirds’ approval.

Mr. Maldonado, who like his Republican colleagues loathed the idea of tax increases, leveraged that power this week to extract what he wanted: the open primary bill, legislation that would bar lawmakers from getting raises while the budget runs a deficit and elimination of a gasoline tax the governor and Democrats had called a fait accompli.

In an interview earlier this week, an exhausted Mr. Maldonado, who is among the more dapper of Sacramento’s lawmakers, said that changes in how people are elected would result in better budgets.

Senator Elaine K. Alquist, of San Jose, said: “He’s had a record of being able to diverge from his party and be more of an independent thinker. He has a great political future. I’m saying this as a Democrat.”

Mr. Maldonado, the son of a field worker, grew strawberries before entering politics and now farms broccoli and cauliflower. In his 20s he served on the City Council of Santa Maria and then as mayor before being elected to the State Assembly in 1998. When term limits ended his Assembly membership in 2004, he successfully ran for the Senate.