Heading into the final stages of the 2012 campaign, the super PAC in position to have the biggest impact, by far and away, is American Crossroads, Sunlight's Follow the Unlimited Money tracker shows.

Of all the outside spenders who filed monthly reports Thursday with the Federal Election Commission, the super PAC founded by veteran Republican strategists Ed Gillespie and Karl Rove, has by far the biggest stockpile of cash: more than $32 million. The intriguing question: Will Crossroads, which has spent $25 million so far opposing President Barack Obama's reelection, continue to invest in the presidential race, or will it begin to detonate money bombs in some of the congressional races where it has been playing, such as the Senate races in Virginia, New Mexico and Nevada?

The reports filed this week with the FEC cover through the end of August and were required from committees that do their accounting on a monthly schedule. Nonprofits and other dark money groups don't file these reports. Other campaign committees — including the campaigns of most congressional candidates — will file reports next month covering the third quarter of this year. But most of the big outside spending committees are monthly filers and a look at who had the most money heading into fall is revealing.

Number two on the list, albeit lagging far behind Crossroads, is House Majority PAC, a super PAC founded by former Democratic congressional staffers to help elect Democratic House candidates (mostly, a look at the group's spending reveals, by trashing GOP opponents). The super PAC backing Mitt Romney comes in third, but its cash reserves don't appear to be enough to enable the GOP presidential hopeful to catch up to a flush Obama, especially given the banner month enjoyed by Priorities USA, which in August outraised Restore for the first time.

Also striking is how many of the top ten committees are groups playing in congressional races, where late, large expenditures can have a big impact. Among these is the newly created American Unity PAC, heavily funded by pro-gay marriage GOP donor Paul Singer. It is promising to back GOP House candidates who back gay rights.