AMERICANS WHO are worried about the corrosive power of big money in politics ought to watch what is about to happen in the Senate. On Monday, a cloture vote is scheduled on legislation that would require the disclosure of donors anonymously pumping tens of millions of dollars into this year’s presidential and congressional campaigns. Not a single Republican in the chamber has expressed support for the bill, known as the Disclose Act, meaning it will probably die for this session. It should be interesting to hear how the Republican senators justify this monumental concealment of campaign cash.

Before the Watergate scandals — for those who may not recall — money ran wild in American politics. One man, W. Clement Stone, gave more than $2 million to President Richard M. Nixon’s 1972 reelection campaign. The Watergate break-in was financed with secret campaign contributions. Fat cats plunked down cash for ambassadorships, and corporations for special treatment. The scandal led to landmark campaign finance reforms, enacted in 1974. For many years since, Republicans and Democrats broadly supported the idea of full disclosure.

That consensus has broken down and thrown the country back to the unruly days before Watergate. We seem to have created the political equivalent of secret Swiss bank accounts. The Supreme Court’s 2010 Citizens United decision opened the door to unlimited donations by corporations, wealthy individuals and labor unions. The sheer size of the donations flowing into groups sponsoring political advertising is alarming enough. But the secrecy is also corrosive for democracy. Who is writing checks for $10 million or $1 million at a single throw, and what do they want? We don’t know, and this shadowy bazaar undermines our political system.

Until recently, Republicans supported full disclosure. Now that the tide of money is running in their favor, they don’t. Their rationale is that exposure might squelch the constitutional rights of donors. In fact, the court has upheld the constitutionality of disclosure. The Disclosure Act is a reasonable bill that would, among other things, require identification of donors of $10,000 or more to certain organizations that spend money on political campaigns.

Credibility is a precious thing. In their lust for contributions, in cozying up to the moneybags of this era, candidates and political operatives in both parties seem to be forgetting that they put their own credibility at risk. There is a very good chance that when some government decision or vote comes along next year, responsible politicians will find themselves haunted by the secret money of the 2012 campaign.

Is it really worth it? Do these donors deserve to remain hidden? Why can’t they handle a little sunshine? We’d like to see a few courageous Republicans rise in the Senate on Monday and declare: Enough is enough.