Grover Norquist’s iron grip over much of the Republican Party is somewhat puzzling. Why should Senators and other lawmakers listen to a guy caught laundering money for Jack Abramoff?

But consider Norquist’s tax pledge and political power another way: that he’s just a proxy for the powerful interest groups that finance him. In the nineties, it was big tobacco that used Norquist’s tax pledge as a cover to lobby lawmakers against cigarette taxes (Norquist still uses an e-mail system donated to him by Altria to send out Tea Party action alerts against tobacco taxes). Now, big PhRMA and other industry groups provide grants to Norquist while his foundation endorses other giveaways, like protectionist support against importing cheaper drugs from Canada and the classification of tax subsidies to refineries as “tax cuts” that must not be cut.

I took a look at the last available budget numbers for Americans for Tax Reform, Norquist’s group. Though they do not reveal their donors, we can cobble together much of Norquist’s donors using foundations and other nonprofits that donate money to him.

The disclosures show that only two billionaire-backed groups have provided over 66 percent of Norquist’s funding:

• The Center to Protect Patients Rights donated $4,189,000 to Americans for Tax Reform in 2010, 34 percent of the group’s budget that year.

• Crossroads GPS donated $4,000,000 to Americans for Tax Reform in 2010, 32.46 percent of the group’s budget that year.

The Center to Protect Patients Rights is the foundation used by the billionaire clique led by the Koch brothers to distribute grants to allied groups. In 2010, wealthy moguls like Steve Bechtel of Bechtel Corporation and Steve Schwarzman of the Blackstone Group met behind closed doors to help lend money to these types of efforts.

Crossroads GPS is the undisclosed group run by Karl Rove. The only known donors are folks like Paul Singer, the “vulture” hedge fund king who benefits enormously from tax strategies like the carried interest loophole. Norquist’s pledge largely benefits billionaires like Singer and Schwarzman, who pay almost nothing in payroll taxes and likely pay a lower rate than their secretaries.

When Norquist promises consequences for the few GOP members willing to break with his pledge, what he’s really saying is that his donor network will retaliate with attack ads and money for primary challenges.

So as our country descends into a position where now 1 percent of society owns more than one-third of the wealth, it should be no surprise that the guy preventing any equitable tax system is fully financed by the privileged few at the top.

Lee Fang is an investigative reporter for The Nation. He last reported that a Congressman leading “fiscal cliff” talks just accepted a job as a lobbyist.