The Senate is expected to vote again tomorrow on the DISCLOSE Act, the bill passed by the House and supported by the President to counteract the damage done to our elections by the Supreme Court’s decision in the Citizens United case. For those just tuning in, that case said that corporations have the right to spend unlimited amounts of money on independent expenditures in elections. The DISCLOSE Act would create a transparency regime so that corporations, unions and wealthy individuals who want to advance their own agenda by paying for independent expenditures could not do so while hiding their real identity.

In the weeks since the Senate’s last vote on the bill, what had been mere speculation that hidden money would shape the 2010 election season has become a cold hard fact. My colleague Paul Blumenthal wrote about a comprehensive report by Public Citizen that found that, “after nearly 100 percent of groups revealed the donors funding their electioneering communications in the 2004 and 2006 election cycles, fewer than 50 percent did so in 2008. In the primary season of the 2010 election cycle, fewer than one-third of groups disclosed their funders.”

Reporting by the New York Times also demonstrates that billionaires and privately held companies are likely behind some of the attack ads that aired during the primaries. Americans for Prosperity spent about $1.5 million helping Republican House candidates in recent months, but because it is a 501(c)(4) organization under the tax code, we can’t be sure where its money came from. (Billionaire David Koch is chairman of its sister organization, Americans for Prosperity Foundation.) Likewise, Crossroads Grassroots Policy Strategies, with its ties to Karl Rove, has spent millions of dollars on negative ads against Senate Democrats, but without having to disclose who is paying for the attacks.

How much more proof do the bill’s opponents need that secret money is playing a significant role in November’s elections? This time, it’s flowing to the right. But without a legislative fix, Republicans who killed the bill over the summer should not count on being insulated from future attacks paid for by anonymous funders. By 2012, left-leaning individuals and groups that want to impact the election without leaving fingerprints may take a page from the Karl Rove playbook and funnel undisclosed money to flood the airwaves with ads that target Republicans.

In the end, which party suffers more losses at the hands of wealthy secret donors is irrelevant. The real victim is the American voter, who, because of the unwillingness of some to pass a transparency measure earlier in the year, will be left in the dark about who is paying for the upcoming elections. The Senate is one vote shy of the 60 it needs to move the bill forward, and the hope is past advocates for cleaner campaigns, including the two Senators from Maine, may step up and vote in favor of the DISCLOSE Act so that, in the future, secret wealth won’t be used to manipulate the system, or our elections.