The 2012 elections shattered spending records, with outside groups such as super PACs, nonprofits, unions and corporations plowing an estimated $1.3 billion into federal campaigns. With this year's elections just two weeks away, we've rounded up some of the best investigative reporting on campaign finance. The list includes stories that provide fresh insight into what happened in 2012 and ones that get inside who's shelling out on campaigns this cycle. In addition, we've spotlighted a couple of ProPublica's stories on the subject.

A Campaign Inquiry in Utah Is the Watchdog's Worst Case, The New York Times, March 2014

John Swallow used to work as a lobbyist for a Utah payday-lending company. So when he decided to run for state attorney general, he turned to payday lenders to help finance his campaign. But Swallow was wary of the industry's sketchy reputation, Times reporter Nick Confessore wrote. "The solution: Hide the payday money behind a string of PACs and nonprofits, making it difficult to trace donations from payday lenders to Mr. Swallow's campaign." Swallow's tactics eventually triggered investigations by the Internal Revenue Service and the state, and Swallow resigned less than a year after his election.

Pro-Obama Group Fires Fundraiser Who Diverted Felon's $100,000 Gift, NBC News, February 2014

Last December, a New Jersey doctor who had been convicted of Medicare fraud and tax evasion back in 1991, applied for a presidential pardon. Two months later, he wrote a $100,000 check to Organizing for Action, a nonprofit formed to promote President Obama's policies. Though the group is not required to disclose its donors, it has a policy of doing so. Samantha Maltzman, an OFA consultant, returned the check and asked the doctor to donate instead to America Votes, another liberal nonprofit that does not make its donors public. Maltzman was fired after NBC News started asking questions.

Tea Party PACs Reap Money for Midterms But Spend Little on Candidates, The Washington Post, April 2014

Cutting wasteful government spending is a core tenet of the Tea Party movement. A Washington Post analysis, however, "found that some of the top national tea party groups engaged in this year's midterm elections have put just a tiny fraction of their money directly into boosting the candidates they've endorsed," the Post's Matea Gold wrote. The Senate Conservatives Fund, for instance, "paid a luxury interior design firm more than $52,000 last year to paint and decorate its Capitol Hill townhouse office."

Meet the New Kochs: The DeVos Clan's Plan to Defund the Left, Mother Jones, January 2014

The billionaire DeVos family exercises huge influence over Michigan politics. In this story, reporter Andy Kroll shows how Dick DeVos Jr. worked to craft a strategy to pass right-to-work legislation in the labor-friendly state and poured money into the effort. "DeVos worked the phones all the way to the end, even calling several lawmakers on their cellphones as they prepared to cast their votes," Kroll wrote. The bill passed, and DeVos has called his strategy a playbook for similar efforts in other states.

Deadlock by Design Hobbles Election Agency, The Boston Globe, July 2013

It's almost a cliché that the Federal Election Commission is broken. The commission, created after Watergate to investigate potential campaign finance abuses, has been deadlocked in recent years by disagreements between its three Democratic and three Republican commissioners. The Boston Globe's Christopher Rowland dug into what causes the paralysis. A Democratic commissioner told him one of her Republican counterparts — whose office is next door to hers — never returned her calls. The number of enforcement actions taken by the agency has plummeted. In one case, the commission's staff found that a wealthy friend of Mitt Romney's had made a $150,000 in-kind contribution to his campaign, far above the $2,600 limit for such gifts. "But the three Republican commissioners disagreed," Rowland reported, "saying Romney's friend merely acted 'in behalf of' Romney's 2008 campaign — not the illegal 'on behalf of' — and thus the flight was allowed."

Koch World 2014, Politico, January 2014

The network of politically active nonprofits — sometimes called dark money groups — with ties to billionaire brothers Charles and David Koch handed out almost $264 million in the 2012 election cycle. In this story, reporter Ken Vogel outlines what the Koch network has planned for 2014 and beyond. The network has distanced itself from Sean Noble, the consultant who ran much of the operation in 2012, and is wading into Republican primaries for the first time. Since the story appeared in January, the Koch network has also launched a super PAC, which — unlike the network's dark money groups — must disclose its donors. They include a New York hedge fund billionaire and an Arkansas poultry magnate.

The Dark Money Man: How Sean Noble Moved the Kochs' Cash into Politics and Made Millions, ProPublica, February 2014

Sean Noble was a little-known chief of staff for an Arizona congressman before he was plucked from obscurity by Charles and David Koch. In the run-up to the 2012 elections, Noble distributed almost $137 million of anonymous cash as the head of the Center to Protect Patient Rights, the social welfare nonprofit at the center of the Koch network. The money found its way into elections all over the nation, from groups supporting Mitt Romney to a group blaming Obama for high gas prices. Along the way, Noble directed almost $24 million to his own companies. The earnings helped him buy a Washington condo and build an eight-bedroom, eight-bathroom vacation home in Utah with five fireplaces.

Corporations Have Found Yet Another (Secret) Way to Help Get Politicians Elected, The Huffington Post, July 2014

Super PACs are required to disclose their donors to the Federal Election Commission, but the donors themselves can be almost completely opaque. In 2012, for instance, a super PAC supporting Ohio Secretary of State Jon Husted received $250,000 from a limited liability company called American Dream Fund LLC. Who's behind American Dream Fund? No one knows. The company was set up six months earlier by a professional incorporation firm called CT Corporation System, and there's no trace of who hired CT to do it. It's another (completely legal) strategy that enables donors to give secretly.

In Wisconsin, Dark Money Got a Mining Company What It Wanted, ProPublica, October 2014

When a Florida company proposed building an iron mine in Wisconsin, it touted the hundreds of jobs the project would generate. But the company wanted something in return — a change in Wisconsin law to speed up the process for getting a mining permit. A court filing accidentally made public in August revealed that the company had given $700,000 to a dark money group that poured money into a critical state senate race in 2012. The targeted senator lost her race, and the company got the law it wanted.

Bobby Jindal's Political Appointees Have Showered His Campaign with Cash, The Times-Picayune and Fox 8 News, November 2013

On March 3, 2011, a Louisiana river pilot named Robert Heitmeier wrote a $1,400 check to Gov. Bobby Jindal's campaign. Less than three weeks later, Jindal appointed Heitmeier to chair a state board that investigates misconduct by river pilots. The donation was one of 317 made by Jindal appointees, their families and their companies identified by the Times-Picayune and Fox 8 News as part of their "Louisiana Purchased" series. The donations totaled more than $1.8 million — a substantial sum in state politics.

More about campaign finance: Read more about money influencing elections in our Q&A on dark money in the 2012 campaign. For details about the history of campaign finance regulations, watch our music video.

What did we miss? Let us know which stories you would include in the comments section below.