This post is being kept up-to-date. It was first published on Aug. 20, 2012.

On Tuesday, the Supreme Court agreed to hear a case challenging caps on overall campaign contributions. The new case could become the most important since the 2010 Citizens United decision, which opened the way for record levels of election spending last year.

From the history of corporate cash in campaigns to Obama’s shifting stance on money in politics, here’s an update on our roundup of the most important stories on campaign finance, and the dark money groups that don’t have to report their donors.

RISE OF DARK MONEY

Karl Rove’s Dark Money Group Promised IRS It Would Spend ‘Limited’ Money on Elections, ProPublica, December 2012
In December, ProPublica obtained a confidential application for tax-exempt status from Karl Rove’s Crossroads GPS. The documents showed that Crossroads, which spent more than $70 million on the 2012 election, told the IRS that its political spending would be “limited.” Crossroads is just one of many social welfare nonprofits spending money to influence elections, while keeping their donors secret.

How dark money helped the GOP keep the House, ProPublica, December 2012
While many observers have noted that mega-donors like Sheldon Adelson backed losing candidates in the 2012 campaign, a close look at the Republicans' effort on redistricting suggests something else: The hundreds of millions spent this year on presidential TV ads may not have hit the mark, but the relatively modest sums funneled to redistricting paid off handsomely.

The IRS's 'feeble' grip on big political cash, Politico, October 2012
Americans for Prosperity, a conservative nonprofit backed by the Koch brothers, spent millions on ads targeting Democrats in the 2012 election. But in the group's original application to the IRS for recognition as tax-exempt, it said it wouldn't spend a cent on politics.

How dark money groups spend millions on elections and call it public welfare, ProPublica, August 2012
Nonprofit groups that don’t pay taxes and aren’t required to disclose their donors are pouring more money into political ads in the 2012 campaign than any other outside group. Some of these groups have claimed not to engage in political activity when applying for their tax-exempt status with the IRS, but later spent millions on political ads. A closer look at the activities of 106 nonprofits active in the 2010 election cycle illustrates lax oversight over such activities.

Follow the Dark Money, Mother Jones, July 2012
Mother Jones charts the history of dark money in politics, from the cash-stuffed suitcases of the Watergate-era to the rise of the modern super PAC.

Tax-Exempt Groups Shield Political Gifts of Businesses, New York Times, July 2012
While the preisdent of insurance giant Aetna was proclaiming support for health insurance reform, his company was funneling millions of dollars to conservative groups working to strike down the legislation. By donating to nonprofits rather than super PACs, companies are able to“quietly push for their political agendas without being held accountable for it by their customers.”

Dark Money groups target voters based on their Internet habits, ProPublica, July 2012
The television ads produced by Crossroads GPS and Americans for Prosperity get plenty of media coverage. But they’re also active online--and these ads get far less scrutiny. Both dark money groups have adopted sophisticated new online advertising tactics to target specific slices of the electorate--and they don’t have to disclose which people they’re targeting, or why.

When the GOP tried to ban dark money, ProPublica, March 2012
Political spending by 501(c)(4) “social welfare” groups exploded in the wake of the Citizens United decision, but the groups have been used in elections in the past. A little more than a decade ago, it was Republicans— including Sen. John McCain, R.-Ariz., and Rep. Amo Houghton, R-N.Y. — who supported a measure to force such groups engaging in political spending to disclose their donors. But the short-lived effort in 2000 to shine light on dark money never got off the ground.

CITIZENS UNITED

Obama flip flops on money in politics, ProPublica, January 2013
Obama has long been a vocal critic of Citizens United. But when it came to his own campaign and outside groups, his actions said otherwise. We chart Obama’s back-and-forth on everything from PACs to public financing.

The Citizens United Decision, SCOTUSblog, January 2010

Money Unlimited, New Yorker, May 2012
The seminal piece on the story behind Citizens United, the Supreme Court case that opened the doors for super PACs and 501(c)(4)s flooding this campaign. This is a good look at the politics behind the decision, and the evolution of judicial influence on corporate money in politics.

In Defense of Citizens United, U.S. News Op-Ed, February 2012
Super PACs are often slammed for dumping huge amounts of undisclosed money into the 2012 presidential race. But Bradley Smith, one of the most widely-quoted supporters of super PACs, says the Citizens United decision, and its ramifications, is actually good for democracy.

How much has Citizens United changed the game?, New York Times, July 2012
Citizens United was undoubtedly a landmark decision in campaign finance, but Matt Bai of the New York Times argues that the influx of outside money in U.S. campaigns originated with the passage of McCain-Feingold in 2002, which diverted unlimited “soft money” contributions from the parties to “rich ideologues with their own agendas.” The ultimate result: “Candidates and parties who become the vehicles of angry outsiders, as Mitt Romney is now, don’t really have control of their own campaigns anymore; to a large extent, they are the instruments of volatile forces beyond their own reckoning.”

SUPER RICH, SUPER PACS

Missouri Political Donor Thrives With No Limits, New York Times, October 2012
The Supreme Court has agreed to hear a case on limits to overall campaign contributions, but four states have no such cap. That has allowed one Missourian to become the state’s “most influential private citizen,” by donating millions to shape debates around teacher tenure and income tax.

Covert Operations, The New Yorker, August 2010
This 2011 National Magazine Awards finalist profiles the billionaire Koch brothers, who are using their money to try to promote libertarian ideals. The resulting “ideological network” of foundations, think tanks and political movements (such as the Tea Party) has become so sprawling that in political circles it’s known as the “Kochtopus.”

How Super PACs are overpowering candidate campaigns, Campaigns & Elections, Sept. 2011
An interesting look at the evolution of super PACs, as political consultants tested the boundaries of a new political advertising model in the 2010 midterms and the lessons learned for 2012.

Texas billionaire doles out election’s biggest checks, Wall Street Journal ($), March 2012
Harold Simmons is one of the 2012 campaign's biggest donors, with most of his money going to super PACs like American Crossroads. In a rare interview, Simmons describes his giving as “for the good of the country” and details his relationship with GOP strategist Karl Rove. “Karl won’t waste my money,” Simmons said. 

The Attack Dog, The New Yorker, February 2012
Larry McCarthy, the media consultant who helps run the pro-Romney super PAC Restore Our Future, is Washington’s go-to guy for negative ads. He rose to prominence with the racially charged Willie Horton ad that helped George H.W. Bush get elected in 1988.

SUPER PACS, RIGHT AND LEFT

Can the Democrats Catch Up in the Super PAC Game?, New York Times Magazine, July 2012
This profile of the largest pro-Obama Super PAC focuses on how the former White House staffers who run Priorities USA Action are trying to convince rich  Democrats “to get over their distaste for the Citizens United decision and their frustration with the president and write a very large check.”

Obama Campaign and Super PAC Create Very Similar Ads, CBS News, August 2012
A look at two different anti-Romney attack ads, one produced by the president’s campaign, and one produced by the Super PAC that supports Obama, but is not legally allowed to coordinate with the campaign. Both ads featured the same man, Joe Soptic, a steelworker who lost his job when Bain Capital shut down a Kansas City plant. “While using the same steelworker in an ad may seem like coordination, it's just the latest example of how narrow the rules are,” CBS reported.

Liberal Fat Cats Wimp Out, The New Republic, July 2012
Why are Democrats so far behind in fundraising? The New Republic counts the reasons, including “we’re not as rich as they are,” Wall Street’s abandonment of Obama, and a general squeamishness among liberals about super PACs. “Why would anyone want to give $5 million to a super PAC to elect a president? It’s incomprehensible,” said one bundler.

Fine Line Between ‘Super PACs’ and Campaigns, New York Times, February 2012
Super PACs and campaigns legally can’t coordinate, yet several groups working for both the Romney campaign and the pro-Romney super PAC Restore Our Future share an office suite in Virginia. It illustrates the delicacy of the rule, but a founder of a consulting firm working for both organizations insisted that they don’t coordinate. Though he did admit it looked “ridiculous.”

In Republican Race, A New Breed of Superdonor, New York Times, February 2012
About two dozen individuals, couples or corporations have given more than $50 million to Republican super PACs this year. They represent a new wave of super-donors, outlined in this big picture piece, influencing the presidential race. But their motivations remain something of a mystery. (We visualize the super PACs’ biggest donors here.)

The myth of the small donor, Politico, August 2012
Politico chronicles the demise of the small donor, dwarfed by outside fundraising in the 2012 campaign. The Obama campaign, which four years ago ushered a small donor “revolution” and discouraged rich donors from giving to outside groups, has shifted their efforts to wooing big donors in the face of record fundraising by Republicans. “The super PACs have diluted the small donors,” said Paul Begala, a Democratic strategist and super PAC operative. “It’s one of the reasons I think Democrats want to do away with them.”

Where to find ongoing coverage on campaign finance:

Center for Public Integrity’s Daily Disclosure: A daily report on super PACs and nonprofits.

Great Moments in Campaign Finance Disclosure: A Tumblr of dubious FEC filings maintained by Derek Willisof the New York Times.

ProPublica PAC Track: Chart of the biggest super PAC donors for 2012 campaign.

Mother Jones Dark Money: Breaking news, weekly roundups and longreads.

 Tweet #MuckReads Suggest your best campaign finance reading and resources with #MuckReads on Twitter or in the comments below, and we’ll update this guide with the best.