A year ago this week, the Supreme Court made a landmark decision about the role of money in elections -- a ruling so momentous that many are still grappling to take stock of its impact on our political system.

The case: Citizens United. The decision: In a 5-4 vote, the Supreme Court ruled that it was unconstitutional to limit in any way the amount of money corporations can spend on attack ads or other "electioneering communications" to sway a political race.

Before Citizens United, plenty of corporate money had found its way into political PACs and other avenues to influence elections. The court also did nothing to strike down the ban on direct corporate contributions to candidates or political parties.

But the decision opened a massive loophole in our country's already-porous campaign finance system, giving corporations the green light to inject unlimited sums of cash into independent groups -- 527s and 501c4s, references to their IRS tax status -- that can intervene in elections.

After the January 2010 decision, many in the media reported that corporations may be skittish about fully exploiting Citizens United's political windfall, but that proved premature. Millions of dollars began flooding into existing electioneering like Americans for Prosperity, backed by benefactors like the Koch brothers and North Carolina retail magnate Art Pope. New groups like Karl Rove's American Crossroads and American Crossroads GPS were quickly erected to funnel tens of millions of dollars into key congressional races.

A new report released by Public Citizen this week surveys the results:

* Spending by outside groups jumped to $294.2 million in the 2010 election cycle, a nearly four-fold increase from the $68.9 million spent in 2006, the last mid-terms. Nearly half of that ($138.5 million) came from just 10 groups, with the biggest share by far benefiting Republicans.

* In 60 out of 75 congressional races, the candidate benefiting most from outside spending won the race -- a remarkable 80 percent win rate.

* The source of the money flooding into elections after Citizens United largely hidden: Because many of the independent groups aren't required to disclose their donors, barely a third -- 34 percent -- of the groups reported which people and groups gave them money.

As Public Citizen notes, the cloak of secrecy surrounding corporate campaign spending goes against the Supreme Court thinking behind Citizens United, which was that massive corporate spending was acceptable as long as the public knew about it:

Justice Anthony Kennedy's opinion for the majority was based in part on the assumption that any dangers posed by the new flood of corporate spending in elections would be mitigated by disclosure. "This transparency enables the electorate to make informed decisions and give proper weight to different speakers and messages," Kennedy wrote.

The DISCLOSE Act, a bill that would have required non-profit groups to reveal the donors behind their election war chests, failed by one vote last spring in the face of a Senate Republican filibuster.

Although not as widely reported, Citizens United proved decisive in state elections as well. As Facing South documented in a series of reports, three independent groups backed by Art Pope in North Carolina -- Americans for Prosperity, Civitas Action and Real Jobs NC -- spent over $2 million targeting 22 state races, helping fuel the Republicans' capture of the N.C. legislature for the first time since Reconstruction.

Some advocates are calling for a new bill to force disclosure of the donors behind outside election spending, although it faces an uphill climb in the Republican-controlled U.S. House and does little to combat the campaign spending arms race exacerbated by Citizens United.

A more ambitious and effective step, says journalist Katrina vanden Heuvel in The Washington Post, is a system of public campaign financing as proposed in the Fair Elections Now Act, which at its high point had 160 supporters in the House. She argues that the bill draws on the successes that reformers have seen at the state level:

A similar system has been adopted in Arizona, and, in 2007, New York City adopted an intriguing mechanism of public finance in which the city matches small donations at a 6-1 ratio, boosting grass-roots fundraising. The result? According to the New York Times, the changes "drastically curtailed the role of businesses, political committees and lobbyists in campaigns" and, importantly, "caused a major drop in donations from those doing business with the city." Such a system, implemented on the national level, could greatly increase the influence of average citizens.

But the state-based experiments in public financing are under attack. The Chamber of Commerce and other groups have lined up to oppose Arizona's "clean money" election system. In North Carolina, the new Republican majority has pledged to dismantle public financing of races for judges -- even though the system is used by 77 percent of state judicial candidates [pdf] -- and three council of state races.

The groups pushing to dismantle these programs are hardly disinterested observers in the debate: In 2010, the Chamber of Commerce was the most powerful outside group in the country, lavishing over $31 million -- all from undisclosed donors -- on races across the country.

In North Carolina, the connection is even more direct: The key advocacy groups pushing to end "taxpayer-funded elections" -- the Civitas Institute (a sister group to Civitas Action) and the John Locke Foundation -- are largely funded by the family foundation of Art Pope, whose money proved so critical in influencing the state's 2010 contests.

But some advocates are pushing to question the Supreme Court's very assumption that corporations are, legally speaking, people with free speech rights. Last year, Rep. Donna Edwards (D-MD) introduced legislation for a constitutional amendment clarifying that corporations aren't people, saying:

"Justice Brandeis got it right," she noted last February. "'We can have democracy in this country, or we can have great wealth concentrated in the hands of a few, but we can't have both.'"

Given the current political climate, it may be unrealistic to expect such a campaign to yield quick results. But Rep. Edwards and others see it as a way to educate the public and make the case for reform.

The message may already resonate with voters: A Survey USA poll last August found that, when asked whether corporate campaign contributions represent "free speech" or "bribes," 77 percent said "bribes."

But the public's cynicism will only lead to change of voters believe that something can be done -- and in the wake of Citizens United, those favoring a political system that benefits the powerful have a lot more resources at their disposal to keep things that way.