Everywhere you turn in the 2012 election, you hear about the influence of super PACs.

But focusing on how much influence these groups, which can accept unlimited contributions but have to report everything they raise and spend to the Federal Election Commission, are bringing to bear on the race badly misses the point.

If you are looking for the real secret weapon of conservative donors and strategists in the November election, you need look no further than not-for-profit groups like Crossroads GPS and Americans for Prosperity. These groups, which are organized as 501( c) committees and governed by the Internal Revenue Service, are free to accept unlimited donations but, unlike super PACs are not required to disclose the sources of those contributions.

And according to research conducted by the investigative journalism website Pro Publica, Crossroads GPS and Americans for Prosperity alone have outspent all super PACs and party committees on television ads in this election to date.

Here's a chart detailing that spending (and you can read the full Pro Publica report here):

Spending by outside groups in the 2012 election

As the chart above makes clear, while super PACs get all the attention, it's the 501(c)(4) groups that are doing the real financial heavy lifting in the campaign. And, due to the vagaries of IRS law, we'll never know where any of that money came from.