This post was prepared in collaboration with Alexander Furnas and Amy Cesal.

Back in July, Senate Republicans successfully blocked the DISCLOSE Act, which would have required all organizations spending $10,000 or more to reveal their donors. Now we understand why.

Through Nov.1, at least $213.0 million has been spent in the general election by “dark money” groups to influence the 2012 elections. Of that, $172.4 million (81%) has been spent to help Republican candidates, as compared to $35.7 million (19%) to help Democrats. (By “dark money” we mean groups that do not disclose their donors and only are required to disclose their congressional race spending within 60 days of House and Senate elections and their presidential race spending following the national party conventions).

The two graphs below show the breakdown by target (President/House/Senate). The first shows the current totals. The second shows them over time, which highlights how Republican dark money groups have picked up the pace in the last several weeks, while Democratic dark money groups have continued at the same pace, lagging further and further behind.

Top Races

As of our latest calculations, there are now 34 races (12 Senate and 22 House) where dark money groups have dropped at least $1 million.

In the Senate, the five races with the most dark money are: Virginia ($19.0 million), Ohio ($13.1 million), and Nevada ($11.7 million), Wisconsin ($10.4 million), and Montana ($7.5 million). Dark money accounts for more than 40% of the outside money in Senate races in New Mexico (71%), Nevada (47%), Massachusetts (44%), Ohio (43%), and Virginia (41%). For dark money totals in all Senate races, click here.

The partisanship of dark money in 11 Senate races appears below (we’ve excluded Maine because it’s unclear how to score attack ads in a three-way race). What becomes immediately clear is that with the exception of a narrow Democratic advantage in Arizona, Republicans have tremendous dark money leads in almost every Senate seat.

There are now 22 House races with at least $1 million in dark money, including two with more than $3 million – PA-12 ($3.3 million), OH-6 ($3.2 million). CA-10 ($2.6 million), MN-8 ($2.5 million) and MI-1 ($2.3 million) are close behind. Of the races with more than $1 million in dark money, dark money accounts for at least half of the outside money in four: NY-28 (97%), CO-3 (69%), NY-22 ($52%) and NY-23 (23%). In those four races, Republicans account for 99.9% (all but $6,100 of the dark money). For complete data on all House races with outside spending, click here.

The graph below shows the Democratic and Republican dark money in these races. Of the 22 races, only three (MI-4, UT-4, IA-4) have the Democratic candidate with a dark money advantage.

Top Spenders

The five biggest dark money spenders are all Republican groups: Crossroads GPS ($66.9 million), the U.S. Chamber of Commerce ($31.1 million), Americans for Tax Reform ($15.4 million), Americans for Job Security ($12.5 million) and the American Future Fund ($10.7 million). Of the top ten, only the League of Conservation Voters ($8.9 million), and Patriot Majority USA ($5.9 million) spend on behalf of Democrats.

These groups and their spending by chamber are visualized below:

All told, 110 dark money groups have spent money this election. Just about half of the organizations (54) have spent in only a single race, and 87 are involved in five or fewer races. The median total spending is just $81,265. Additionally, 47 (43%) of the dark money organizations have spent less than $50,000 over all, and 56 (50%) have spent less than $100,000. The full list of dark money groups can be accessed here.

Meanwhile, the five most active dark money groups account for 64% of the dark money spending, and the ten most active groups account for 80% of all spending. Alone, Crossroads GPS and the Chamber of Commerce account for 46% of the spending by groups who don’t disclose their donors and only report their spending just before the election.

Looking more closely at the dark money groups spending in the Senate, we can see that National Federation of Independent Businesses (NFIB) contributes in the most different races (14), but spends very little in each. The Chamber is involved in 13 races, spending almost $2 million per race, and Crossroads GPS is involved in 10 races, spending an impressive $4 million per race. The most active Democratic group in the Senate, Priorities USA spends almost $1 million per race and has been active in five races.

In the House, the dark money group active in the most races is the National Rifle Association (NRA), but on average it spends only about $16,000 per race. By contrast, Americans for Tax Reform is involved in only 14 races, but it spends almost $1 million per race it is involved in.

Mousing over the different dots in the above graph gives a good sense of the variety of strategies that dark money groups use. Many contribute substantial amounts in just a few races. Others contribute small amounts in many races. Only a few go big in many races.

Only a partial picture?

These totals surely undercount the true amount of money these dark money groups have spent to influence elections, since they only have to disclose their election-oriented spending within 60 days of an election in House and Senate races, and following the national nominating conventions in the presidential race. Yet, when we looked at what Crossroads GPS was doing earlier in the cycle, we found that as of July 5, they had already announced $83 million in ad buys – more than they’ve reported in the disclosure window we are able to cover here. Additionally, since 501(c)(4) “social welfare” groups like Crossroads GPS, 501(c)(5) union groups like AFSCME, and 501(c)(6) trade association groups like The Chamber of Commerce are not technically political committees and under Federal Elections Commission jurisdiction, they do not have to disclose their donors.

Overall, dark money represents about 22% of the total outside money. The reported super PAC spending in the general election now is at $459.0 million, still more than double the reported dark money. Super PACs have to report all of their spending regardless of the timing. They also have to report their donors.

Ultimately, we will probably never know where this dark money comes from, nor the true spending numbers. All we know is there is a tremendous amount of it — $213 million (and counting) that has been reported, and more than $1 million (and counting) in 12 Senate and 22 House races. We also know it overwhelmingly (4-to-1) is on behalf of Republicans.

For the underlying data that powered these charts, click here.

To keep track of the latest totals on all outside spending, be sure to check back with our Follow the Unlimited Money site.