Estimate: Nearly $6 billion will be spent on elections this cycle

Total political spending on elections this cycle is estimated to reach nearly $6 billion, according to an analysis by the Center for Responsive Politics, a nonpartisan group that tracks the influence of money in politics.

The researchers who compiled the report gathered data through public disclosure documents submitted to the Federal Election Commission and tax documents filed by nonprofit groups that are not required by law to disclose their donors. The estimated amount—$5.8 billion—is $400 million more than the record-breaking amount spent in the last presidential election cycle in 2008. The report includes spending on congressional campaigns in its calculation and estimates that the presidential race alone will cost $2.5 billion.

"Although a lot of money still remains to be raised and spent, the data already show that we're on track to break the extraordinary, record-setting sums spent in 2008," said CFRP Executive Director Sheila Krumholz. "That cycle was the first in which we crossed the $5 billion mark, and the big question now is whether we will already reach—or surpass—$6 billion just one cycle later. At a minimum, we'll come close."

Since certain nonprofit groups that spend on campaign speech are not required by law to provide comprehensive reports on their activity, the estimate is not perfect, the researchers said.

Outside spending, the researchers who compiled the report wrote, "is a wild card that makes predictions tricky."

From the report, here's a breakdown of which groups are spending the most this cycle:

Business interests accounted for about 77 percent of all contributions, with ideological, labor and other interests accounting for the remainder.

Broken down by sector, the finance, insurance and real estate sector once again dominates the world of political contributions with a total of $348.5 million thus far, including contributions from individuals and PACs to candidates, parties and outside groups as well as corporate contributions to outside groups. Within that sector, the securities and investment industry, or Wall Street, has given $144.2 million. In both cases, 63 percent of the funds to candidates and party committees went to Republicans.

In the presidential race alone, Wall Street's loyalties are clear: Those employed in securities and investment have given $10.5 million to Mitt Romney and $3.8 million to President Barack Obama.

The report says that among industries and interest groups that donated to candidates, party committees and outside groups, retirees contributed the most with $178.9 million in the first 18 months of the cycle. Securities and investment came in next with $144.2 million, and lawyers and law firms were third with $114.2 million.