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This year, television viewers in Pennsylvania are being bombarded by an ad attacking Senate candidate Joe Sestak for, among other things, gutting Medicare. The ad — which the non-partisan watchdog group FactCheck.org calls "badly misleading" — is funded not by Sestak's opponent but by an independent group called Crossroads GPS.

OPPOSING VIEW: Hands off political speech

Such ads have long been common in American politics. But this election season, the amount of money flowing into them is skyrocketing, thanks in part to a Supreme Court ruling earlier this year that gave corporations and labor unions the right to spend unlimited amounts to back or attack individual candidates.

The Center for Responsive Politics, a group that follows political spending, estimates that at least $3.7 billion will be spent on this year's congressional elections, almost $1 billion more than was spent in 2006.

Even more troubling than the amount of money is that it is increasingly being channeled through non-profit groups that do not have to disclose their donors.

The group running the Sestak ad, and several ads like it in other states, is affiliated with Karl Rove, a longtime Republican political operative and aide to former president George W. Bush. Because it is structured as a 501(c)(4) organization— similar to non-profit groups that might support education or the arts — it is not required to reveal its funding sources. The same goes for a number of other groups with benign-sounding names— Americans for Job Security and Patriot Majority, to name just a couple— that are littering the political airwaves.

This noxious mix of unlimited money and secrecy means that Americans have no idea who is trying to buy this year's elections. Some of these ads could be underwritten by a single industry, a single company, or even a single person with a vendetta. Big money can easily promote a big lie. The closer to election day, the less chance the candidate under attack has to expose the truth. As the process is fully exploited, candidates almost certainly will find themselves facing veiled, or not so veiled, threats to vote a certain way or face a possible onslaught of anonymous attacks.

This emerging system is a transparent boon to special interests, a massive barrier to honest politicians and a sure loser for the public. Yet Congress — for reasons that will surprise no one — has so far been unwilling to do anything about it.

With the Supreme Court having struck down limits on the size of corporate and union contributions, megamoney pouring into elections is apparently here to stay. But the court's January decision explicitly invited disclosure rules, so more transparency would be an improvement.

Some states already have fairly good disclosure laws, something that Target Corp. found out when it had to reveal that it contributed $150,000 to a Minnesota gubernatorial candidate, prompting a backlash from some Target customers.

But federal legislation is needed as well. Such a measure, called the Disclose Act, is stalled in Congress. Republicans are filibustering the act in the Senate, and Democrats wrecked the House version by allowing exceptions for powerful special interests such as the National Rifle Association, AARP and the Sierra Club.

The irony here is unavoidable. Lawmakers can't rid themselves of anonymous attacks from special interests — because those very same interests won't let them. Until this gets fixed, negative political ads underwritten by shadowy groups deserve to be taken with even bigger grains of salt than usual.