The story of California’s so-called Millionaires’ Tax is the kind of thing that can give a big, bumbling bureaucracy a bad name.

In an election year, it’s also the kind of story that can scare people away from supporting ballot measures that require major tax support, perhaps including potentially beneficial measures.

Here’s the story.

Back in 2004, California voters passed Proposition 63, formally known as the Mental Health Services Act, imposing a 1 percent tax on seven-figure incomes to be used to develop and expand mental health care services.

Not the worst idea, and indeed, in the 12 years since there have been plenty of anecdotes about Prop. 63-funded programs helping Californians overcome mental illness or even heading off cases in people at risk of mental illness.

One problem: The anecdotes are just that. Not statistics. Not hard evidence. Just isolated tales.

So how do voters know if state and local officials and others in charge of spending the Millionaires’ Tax’s $17 billion in aggregate revenue are using it effectively?

We don’t.

That worrisome fact was underscored last week by the release of a report by the Little Hoover Commission calling for “more vigorous accounting” of how $2 billion in annual revenue is spent and better documentation of the results.

(One pictures a wife, greeting her husband as he stumbles drunkenly up the front porch, calling for a “more vigorous accounting” of the $20 bill she gave him to buy milk.)

“The state still can’t provide conclusive data to show how it is keeping promises made to voters in 2004, or to wealthy taxpayers who fund Proposition 63 programs with a 1 percent surtax, and, most importantly, to the individual Californians and their families who rely on these services for much-needed help,” said a letter to state officials from Pedro Nava, chairman of the Little Hoover Commission, the independent oversight agency dedicated to scrutinizing California government operations.

Worse: The state has been warned about this at least three times before — in an Associated Press investigation, a state audit and a 2015 review by the Little Hoover Commission.

The commission noted that the Associated Press found four years ago that some Prop. 63 money was going to general (not mental) health programs, and that lawmakers already have siphoned away revenue for uses probably not envisioned by the voters, including $130 million a year to finance a bond for supportive housing for homeless people with mental illness.

The risk is that if it can’t be demonstrated that the Millionaires’ Tax is paying off as intended, more and more money could be diverted and the original point lost, the Little Hoover Commission said.

State Department of Health Care Services Director Jennifer Kent told the AP her agency is working to address the issues.

But how did it get to this point, and what’s taking so long?

The commission said it sees only partial improvement in financial reporting and oversight of Prop. 63 funds, and weak attempts at improvement because the diffused government programs lack central leadership taking responsibility.

The state Legislature must require better.

While we continue to wait, voters looking at the several tax-related measures on the Nov. 8 ballot must consider how carefully the proposals are designed to account for the money being collected.