By relinquishing a hefty lead in the polls to a super-wealthy opponent, Tom Campbell’s U.S. Senate campaign is becoming the textbook case for how money is not only the mother’s milk of politics — but also how the lack of it is political poison.

Heading toward Tuesday’s primary, rarely has money been such a prominent factor — in some cases seemingly the only important factor — in so many California races.

“And never before have so many candidates been successful by being willing to dig deep into their own pockets,” said Larry Gerston, a San Jose State political scientist.

While candidates such as the GOP’s Campbell have struggled to raise money, saddled by campaign finance laws that restrict how much individual donors can give, there are no limits to what mega-rich politicians such as former eBay CEO Meg Whitman and former Hewlett-Packard Chief Executive Carly Fiorina can pump into their own campaigns. And special interests like PG&E and the San Francisco 49ers can spend as much as they want to push ballot measures, all thanks to free-speech protections.

For all the attempts in recent years to curb the perversity of money in politics, it’s only gotten worse, campaign finance reform advocates say.

All told, Whitman, her opponent in the GOP race for governor Steve Poizner, Fiorina, PG&E and the 49ers have spent more than $145 million to get their messages out.

And then there are the likes of Campbell, who hasn’t contributed a penny to his campaign, surviving on $2.6 million in donations.

His pauper status prompted him to ditch the governor’s race and run for Senate instead, only to be outmatched by Fiorina’s personal spending.

Under federal law, U.S. Senate candidates can raise money in maximum increments of $2,400 per election cycle. By contrast, the donation limit for governor is $25,900 per individual.

The federal limit applies no matter the size of the state or the expense of advertising. California has the same cap as Rhode Island and Wyoming. The cost of one 30-second spot on “American Idol” in the Los Angeles market will buy you a couple of days of statewide ads in Montana.

The $2,400 limit amounts to a severe handicap for Campbell, who lacks the name recognition and extensive donor list of a longtime incumbent like the Democrats’ presumed nominee for governor, Jerry Brown, as well as the large bank account of a Fiorina, Poizner or Whitman. Campbell has raised less than half the amount of Fiorina’s personal contributions.

The reason the limit is so much higher in California is that the state Legislature pulled the wool over the eyes of voters in 2000 when it put Proposition 34 on the ballot, according to Common Cause and the nonpartisan Center for Governmental Studies in Los Angeles.

“The Legislature billed it a measure to limit contributions, but it actually significantly raised limits,” said Bob Stern, president of the center. He and other critics of Proposition 34 say it also spurred the creation of more “independent expenditure” committees, which have no caps on what they can spend to help candidates.

For billionaires, too, the sky’s the limit.

In the landmark case of Buckley v. Valeo, the U.S. Supreme Court in 1976 ruled that limits on campaign contributions were constitutional but that candidates should be able to spend whatever they wish on their own campaigns because it’s a form of free speech.

“It’s that pesky thing called the First Amendment,” said former GOP consultant Allan Hoffenblum, who now edits the California Target Book, which handicaps races throughout the state.

These days, massive infusions of as much as $20 million at a time are a dime a dozen. Consider this:

Whitman’s rapid rise in the polls coincided with her all-Meg-all-the-time radio and TV campaign funded largely by $68 million of her own money. Her huge lead dwindled when Poizner, the state’s insurance commissioner who has thrown in $24.2 million of his own money, fought back with his own TV ad campaign, only to see Whitman ramp up her spending and recapture her cozy lead.

Two polls by the Sacramento publication Capitol Weekly, one released on April 24 and the other on Thursday, tell volumes about the Senate race. The April survey, taken a few weeks before Fiorina launched a heavy TV ad campaign in parts of the state, showed Campbell with a 14-point lead. Fiorina pumped $5.5 million of her own money into the campaign — $3 million in the past month. Thursday’s poll showed her ahead by 15.5 points.