When the U.S. Supreme Court ruled in 2010 that corporations and unions could make independent political expenditures in the infamous Citizens United case, it also made clear that disclosure of who was contributing was not only allowed, but helpful.

The author of the decision, Justice Anthony Kennedy, noted: “This transparency enables the electorate to make informed decisions and give proper weight to different speakers and messages.”

So what’s happened since Citizens United was decided more than two years ago? Nothing.

But a new version of the Disclose Act could change that. It’s coming up for consideration this month in the Senate; senators should pass it and give voters a better idea of who is funding campaigns.

In the wake of Citizens United, American politics is awash in money. The U.S. Chamber of Commerce plans to spend more than $50 million on elections; it doesn’t disclose its donors. And Americans for Prosperity, which also doesn’t reveal its donors, plans to spend $100 million this year. Unions and affiliated groups on the left will spent millions of dollars more.

And much of it will be spent anonymously — and thus unaccountable.

But the 2012 version of the Disclose Act could change that. It is sponsored by Sen. Sheldon Whitehouse, D-R.I., and has 34 co-sponsors — unfortunately, all of them Democrats. It would require groups spending more than $10,000 on election-related advertising to name donors who gave $10,000 or more. Broadcast ads also would have to list the top funders of the groups running the ads.

Republicans in the past have endorsed disclosure. But no more. Senate Minority Leader Mitch McConnell now, laughably, calls this legislation “un-American.”

In an op-ed recently, the Kentucky Republican, in the past a backer of disclosure, embraces the political equivalent of an Internet conspiracy theory.

“Billed as ‘reform,’ the measure is an attempt to identify and punish political enemies, or at the very least, intimidate others from participating in the process — an effort that’s already under way,” he wrote.

In McConnell World, “punishment” is letting the public know how many thousands of dollars donors are giving his side.

We’d call that fairness.

The Disclose Act would apply to all organizations organized as 501(c) or 527 groups. That would include groups such as the National Rifle Association, the Chamber of Commerce and MoveOn — organizations supporting both of the presidential candidates.

“A simple disclosure bill is probably the easiest way to go forward, eliminate the complicated, keep it simple,” Whitehouse told Roll Call recently. “It’s an issue where our Republican colleagues have said over and over and over again that they’re for it.”

And they should be for it again.