SACRAMENTO — Gov. Gavin Newsom helped try to keep California’s proposed billionaire tax off the ballot. Now that Proposition 40 has qualified, he is largely keeping his distance from the fight. The initiative would impose a one-time 5% levy on the assets of California’s wealthiest residents, with the money intended to offset federal health care cuts. Newsom has argued that the plan would push high earners and their businesses out of California, weakening the state’s tax base and economic competitiveness. Although Newsom remains one of Proposition 40’s most prominent opponents and has been briefed by the campaign working against it, he is not raising money for the effort or leading its public messaging. The political calculation is straightforward: a defeat could validate his warnings, while an opposition victory could leave him vulnerable to attacks from the Democratic Party’s left flank. “It feels like a sticky wicket for him,” said Jim Kessler, president of the centrist Democratic think tank Third Way. “A little hand grenade was tossed in his lap with this.” Newsom previously lobbied the initiative’s supporters to withdraw the proposal. His allies also pressed organizations including the California Teachers Association and Planned Parenthood to oppose it. The governor has said California should address inequality through other tax increases while pursuing what he calls a broader effort to “democratize the economy.” But the effort to build a united Democratic opposition has broken down. The California Labor Federation and the California Democratic Party have endorsed the tax, giving supporters institutional backing and making it harder for Newsom to portray the proposal as an economic threat opposed by Democrats across the political spectrum. “The issue’s not great for him politically,” said a Democratic consultant involved in the opposition campaign. “There is a disadvantage for him with many segments of the electorate.” Proposition 40 has become a proxy for a larger Democratic debate over whether the party should pursue aggressive new taxes on the ultrawealthy. That argument is expected to shape the 2028 presidential primary, where Newsom is widely viewed as a potential candidate. Sen. Bernie Sanders and Rep. Ro Khanna, a California Democrat who is also considering a presidential campaign, have cast the measure as a test of whether elected officials are willing to confront entrenched wealth and the affordability crisis. Khanna has linked Newsom’s opposition to the governor’s national ambitions and accused him of protecting an establishment dependent on wealthy donors. “They’re going to put the governor’s face on it, and they’re going to put elected officials’ face on it, and they’re going to fearmonger,” Khanna said at a recent campaign event. The governor has attempted to draw a distinction between rejecting Proposition 40 and opposing higher taxes on the rich generally. After the measure qualified for the ballot, Newsom proposed a series of national tax increases that could become part of a future presidential platform. “There’s not going to be a single Democrat running for president in 2028 that will not have a plan to dramatically increase taxes on the most wealthy,” Kessler said. “How they do it will differ.” Newsom’s aides are involved in the opposition effort, either working within the campaign or communicating regularly with its organizers. One adviser said the governor’s team has ample information about the campaign’s strategy, even as Newsom himself avoids making its decisions. The first opposition advertisement featured Newsom but did not make him the central figure. It also highlighted Republican gubernatorial nominee Steve Hilton, Democratic rival Xavier Becerra, teachers and firefighters — a lineup designed to show voters that opposition extends beyond the governor and his usual political base. “Our task as a campaign is to let voters know, especially Democratic voters, who’s lined up against this measure,” said Anthony York, a spokesperson for the opposition. “When they learn not only Governor Newsom but Xavier Becerra and Steve Hilton are against it, it changes the perception of what this measure does.” Polling has shown Proposition 40 with, at most, a narrow lead. The opposition campaign is being heavily financed by billionaires, including a group led by Google co-founder Sergey Brin, which is pouring tens of millions of dollars into the effort. That spending could give Newsom political cover — but it also underscores the central problem facing the governor. If voters reject the tax, he and his allies can argue that California’s economy cannot be treated as an unlimited funding source. If voters approve it, his opponents will have a ready-made argument that he stood with Silicon Valley’s fortunes against Californians struggling with health care costs and inequality.