A one-time tax on the ultra-rich has set California's wealthiest against its own Democratic establishment, and the billionaires are winning the first round on spend.

"Ro, that's insane. You want the state to loan money to the founder, who will then immediately give it back to the state as a wealth tax?"

— Mark Cuban, in a public exchange with Rep. Ro Khanna over the billionaire tax

California is about to find out what happens when a state says, essentially, "pay up," and a handful of its residents respond by writing a check for their own freedom. Proposition 40, a one-time 5% tax on the net worth of billionaires who were California residents as of January 1, would, if it passes in November, raise tens of billions of dollars for a special account dedicated 90% to public health care. The Legislative Analyst's Office, the state's nonpartisan fiscal watchdog, says the state "probably would collect tens of billions of dollars" over several years, while also warning that departing billionaires would cost California "hundreds of millions of dollars or more per year" in ongoing income tax.

It is a rare ballot fight in which both sides have serious money, but only one side's money comes in $100 million denominations.

The opposition machine is called Building a Better California. On paper it is a broad coalition. In practice it is a handful of tech titans: Sergey Brin, the Google co-founder, has poured more than $100 million into the group. Venture capitalist L. John Doerr has given more than $17 million. Ripple co-founder Chris Larsen, a longtime Democratic donor, has put in $12 million and added another $10 million in an August 14 filing. Eric Schmidt, Google's former chief executive, has given $3 million.

That is at least $156 million into a single cause, most of it from men who will personally be subject to the tax.

Brin, for his part, has done more than write checks. According to NPR, he has moved to the Nevada side of Lake Tahoe, a residence change that does exactly what it is supposed to do: sever the tie that would make him a taxpayer under the measure. He has also compared the proposed tax to the Soviet-style socialism his family fled in the late 1970s. In other words, the man most exposed to the tax has already shown voters where he thinks loyalty ends.

The group's strategy is not simply to defeat Proposition 40. It is to make victory impossible even if the tax clears the ballot box. Building a Better California has already spent more than $127 million qualifying two companion measures: Proposition 41, which would require audits of new special taxes and bar them from being excluded from the state spending limit, and Proposition 42, which would ban new taxes on assets including personal property, intellectual property, and retirement accounts. If 40 passes but either 41 or 42 wins more votes, the billionaire tax is voided.

Translation: the billionaires are not just defending the tax. They are building a demolition crew for it, staffed with their own signature on two extra lines on the same ballot.

This week, the group crossed from ambiguity to combat, making a $5 million donation to the organized opposition campaign, the largest reported gift to that effort so far. The campaign, fronted publicly by teachers and firefighters unions, says it welcomes support "from everyone." The optics matter. Garry South, a Democratic strategist, put it bluntly: "Nobody likes political consultants or lawyers. They like firefighters and nurses and teachers." Billionaires write the checks; blue-collar unions hold the podium.

The tax's advocates are the usual suspects: SEIU-UHW West, the union that collected more than 1.6 million signatures to put the measure on the ballot; the California Federation of Labor; Sen. Bernie Sanders; Rep. Ro Khanna. The California Democratic Party itself backed Proposition 40 in early August, a decision that reportedly split the party.

The splits are the story. Governor Gavin Newsom, a Democrat, opposes the tax, arguing at last year's DealBook Summit that "people have this simple luxury, particularly people of that status: they already have two or three homes outside the state." Xavier Becerra, his likely Democratic successor in the November gubernatorial race, opposes it too. The California Teachers Association and Planned Parenthood Affiliates of California are against it. Nine Democratic state lawmakers sent an open letter last week saying the measure, "while well-intentioned," would "blow a massive hole in our state budget in the years ahead."

Even within the yes camp, the fights have gotten personal. Khanna proposed that the state could make loans to billionaires whose wealth is tied up in illiquid company stock, letting them pay the tax over time. Mark Cuban, a billionaire who has donated to Democrats, called the idea "insane" and "the biggest [insult] in the history of entrepreneurship. Ever." If the tax passes, Cuban added, "only idiot startup founders stay in Cali."

A tax designed to make the rich pay has so far accomplished one thing with precision: it has made the rich angry, organized, and specific about the politicians who support it.

The numbers behind the fight are worth pausing on. California is home to more than 200 billionaires, more than any other state, and their collective wealth jumped from $300 billion in 2011 to $2.2 trillion by last October, according to the law and economics professors who helped draft the measure. Forbes now counts a global record 3,428 billionaires on Earth. In June, Elon Musk briefly became the first person ever to pass a trillion dollars in net worth after SpaceX went public. Meanwhile the share of American economic output going to workers has fallen to a record low, 52.9%, according to Reuters data: for every $100 the economy produces, workers take home $52.90.

Polling is the one number the billionaires cannot buy. PPIC's May survey found that 54% of likely voters favor a one-time tax of up to 5% on taxpayers and trusts with covered assets over $1 billion. The measure passed the signature threshold with more than double the signatures it needed. Voters are not, so far, convinced that the richest people in the state should be exempt from the basic arithmetic of a state that is losing billions in federal Medicaid money, sees 3.4 million Californians at risk of losing Medi-Cal coverage, and cannot afford a $1 million house in Los Angeles.

That majority is why the opposition is spending the way it is. $100 million to defeat a tax that would cost its chief donor $13 billion is a return on investment of roughly 130 to 1. In the history of American politics, few defenses of the existing order have been so candidly, profitably organized.

The deeper point is that Proposition 40 is the first test of a global movement, not just a California tax bill. New York's mayor has proposed a 2% income tax on earners over $1 million. Washington, Maine, and Minnesota have passed or are weighing similar measures. In the United Kingdom, 120 millionaires have signed a "Proud to Pay" letter begging the government to tax their wealth. Every one of these fights will run into the same wall California is building right now: the ultra-wealthy can move, can lobby, can buy the unions' credibility, and can fund measures that kill the tax after it passes.

Brin has already shown how. He does not need to win the argument. He needs to show that winning has a cost, and that the cost is payable. The question November will answer is not whether the billionaires can spend. They have shown they can spend. The question is whether 40 million Californians, voting on a state that is running out of money, care enough about their own hospitals to keep paying attention while the other side's ads are running.

The billionaires have $156 million and a demolition crew. The rest of California has the ballot. That is the entire fight in one line, and for once, the money is on the side that already owns everything.