Here’s a simple idea that both parties should agree on: disclosure. Anybody who contributes money to influence an election — corporations, unions, advocacy groups, individuals — should be required to tell voters what they’re doing. Then they can be held accountable for their actions.

Nothing in Washington is simple, however, or free from partisan wrangling. Current law contains a huge loophole. Millions of dollars in anonymous donations are flooding the campaign landscape. But Republican filibusters have blocked every legislative attempt to close that breach.

Almost 99 years ago, Justice Louis Brandeis famously wrote, “Sunlight is ... the best of disinfectants.” He was right then and he is right now, yet every day his wisdom is being trashed. The result is a scandal waiting to happen.

After Watergate, a wave of revulsion and reform strictly limited individual contributions to campaigns (corporations and unions had long been barred from financing candidates) and required public disclosure of those donations.

Then the U.S. Supreme Court’s 2010 decision in the Citizens United case allowed unlimited donations from any source to so-called super PACs, which could participate in elections as long as they did not directly “coordinate” their efforts with the campaigns they were supporting. The rule is a fraud, of course; there’s plenty of coordination, but at least the super PACs have to reveal their supporters.

But money in politics is like water: It finds the cracks in any law, and the smart folks in both parties are using a provision of the tax code called 501(c)(4) to wedge open those cracks. Under this clause, organizations devoted mainly to “social welfare” can spend money on campaigns as long as politics is not their primary purpose. And they do not have to reveal their donors to anyone.

The whole system is sneaky, shadowy and downright un-American. If a coal company contributes to a candidate who opposes clean-air rules, voters deserve to know that. If a teachers union tries to defeat a legislator who wants to restrict its bargaining rights, that should be public, too.

Sen. Charles Schumer, the New York Democrat who has sponsored legislation to close this loophole, got it right when he said, “All we’re saying is that if you attack us, put your name on the ad.”