"Convincing voters to tax themselves is always an uphill fight, but every one of these incidents over the summer makes his path a little bit steeper," said Dan Schnur, director of the Jesse M. Unruh Institute of Politics at the University of Southern California and a former Republican consultant.
The high-speed rail plan, which has come under intense criticism, already has been targeted by the opposition campaign, which seized on the summer's missteps as evidence that politicians can't be trusted with more tax revenue.
The No on 30 campaign released an Internet video coinciding with the end of the Legislature's summer recess to "welcome politicians back from vacation," using television coverage of the scandals and misspending.
"All of these issues speak to the management of our tax dollars in Sacramento ... and that is a part of this discussion on Prop. 30," said Joel Fox, president of the Small Business Action Committee and a spokesman for the opposition campaign.
California voters are generally not inclined to support tax increases and have rejected the last eight statewide measures on the ballot, including a June proposal to raise taxes on cigarettes to fund cancer research.
They are far more likely to support taxes on the rich rather than themselves, but Brown's initiative includes a sales tax hike that undercuts that selling point. This year, he persuaded union supporters to drop a more popular "millionaire's tax" in favor of his plan.
Still, the opposition campaign has anemic funding from business groups that back it compared with the millions from Brown's union allies.
Backers of Proposition 30, which had a slim lead in summertime polls, have raised more than $10 million to date, with millions more pledged by independent supporters. Opponents have collected less than $500,000.
The governor said if voters reject the taxes, he'll follow their will and make deep spending cuts. But he hoped they will be able to focus on the risk to schools if his initiative fails.
"Proposition 30 is only one thing: it's either a yes or a no," he said. "And it's about schools, it's about money, it's about balancing the budget, it's about public safety. And people will decide."
Associated Press writer Terry Collins in San Francisco contributed to this report.
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