Arguments about the role of often-anonymous "outside" money in political campaigns naturally tend to be partisan. Democrats complain about big spending by rich, conservative people and corporations. Republicans say the problem is the millions of dollars given by labor organizations to support liberal candidates and ballot initiatives.

A new analysis shows they are both right.

Consider this a reminder that members of both major parties, to say nothing of the growing numbers of unaligned voters, should fear the effects if campaign-finance rules are loosened further, as many think will happen when the U.S. Supreme Court rules in the McCutcheon v. FEC case about limits on contributors' "aggregate" giving.

Gov. Jerry Brown talks to the media with supporters of Propostiton 30 behind him after casting his ballot at his precinct at Oakland Fire Station 6 in
Gov. Jerry Brown talks to the media with supporters of Propostiton 30 behind him after casting his ballot at his precinct at Oakland Fire Station 6 in Oakland, Calif., on Tuesday, Nov. 6, 2012. (Laura A. Oda/Staff)

Republicans may indeed have been quicker to take advantage of the Supreme Court's 2010 Citizens United decision. But according to the Center for Public Integrity, a nonprofit organization based in Washington, D.C., Democrats more than caught up in 2012 state elections across the nation.

Using data from the National Institute for Money in State Politics on 38 states with significant elections and disclosure laws, the public-integrity group's reporters found unions and other pro-Democratic groups outspent pro-Republican groups by $8 million.

Looking closer at California data, one finds that labor groups' $129.9 million in spending on 2012 races, one-fifth of the year's total campaign contributions, was the most among 14 categories listed. "General business" groups were second with $81.1 million.

Highest on the list of labor contributors: teachers' unions, with $44.9 million, and state and local government workers' unions, with $34.7 million.

Naturally, a lot of that money went to the campaign against Proposition 32, which would have prohibited campaign contributions from payroll deductions. Proponents said it would rein in the power of public employee unions in Sacramento, while opponents argued it was a cynical attempt to silence labor throughout the state. Prop. 32 was defeated.

In the celebrated case of the shadowy $11 million given by an Arizona group to California's yes on Prop. 32 and no on Prop. 30 (tax hikes) campaigns, a recent report showed that not only were voters in the dark about where the money came from, even the Republican consultant in charge of it wasn't sure where it was going.

The Center for Public Integrity found that in the 38 states it studied, money originating with donors from out of state accounted for more than half of the contributions by nonprofit groups, super PACs and others not directly connected with campaigns in 2012.

While the partisan campaign industry might not mind this outside spending and so-called dark money, voters should. Campaigns increasingly relying on big money from faceless donors lessens, sometimes dramatically, the influence of ordinary voters.

Republicans and Democrats alike should see this is no way to run a political system.