The following originally appeared at Huffington Post.

Yesterday, Senate Republicans voted, for a second time in two days, to continue their filibuster of the DISCLOSE Act, a bill that would simply require outside groups spending money on elections to tell the public where their money comes from. At the same time, not surprisingly, Republican presidential candidate Mitt Romney is in hot water for failing to disclose more than the minimum of personal tax returns and lying about his history at the company that made his fortune — all while we know that a portion of his wealth was hidden in infamously secretive Swiss bank accounts.

Senate Republicans and Romney are spending a lot of time and energy this week to keep their financial histories secret. It’s only natural to ask: What do they have to hide?

You would think the DISCLOSE Act would be an easy bill to pass. In fact, many Republican Senators were "for it before they were against it". What it does is simple: it requires any organization — corporation, union, super PAC or non-profit — that spends money influencing elections to report within a day any election-related expenditure of $10,000 or more. It also requires that these organizations make public the names of the individuals and corporations contributing $10,000 or more to fund this election spending. In short, all those front groups that have been pouring money into elections since Citizens United will have to disclose who their major donors are. Voters would know who was trying to tell them what.

This is not a partisan issue. Disclosure requirements, like those in the DISCLOSE Act, were endorsed as constitutional by the Supreme Court majority that handed down Citizens United. Even the conservative justices who saw no problem with more money in politics assumed that disclosure would be a check on the integrity of the election process.

But Republicans in Congress have been fighting tooth and nail to keep DISCLOSE from the books. Why? The fact that they might not want to publicize the motives of some of these super donors, and the fact that the new flood of outside political spending overwhelmingly favors conservatives, might have something to do with it.

Meanwhile, Mitt Romney is having disclosure problems of his own. It’s standard practice for presidential candidates to release their past tax returns — President Obama has made public his returns from the past dozen years. Even Romney called on his gubernatorial opponents in Massachusetts to release their returns. (In a classic Romney flip-flop, when he was later asked to hold himself to the same standard, he said his original demands had been wrong).

The only conclusion to draw from Romney’s tax-return reticence is that there’s something he doesn’t want us to see. The recent revelations that Romney has told conflicting stories about when he left his job at Bain Capital might give us a taste of what he’s kept hidden. And hiding part of his fortune in tax havens like the Cayman Islands and in Swiss bank accounts that have for centuries epitomized financial secrecy doesn’t help.

The issue of financial disclosure isn’t a sideshow to this election — it’s a big part of what this election is about. How can we trust senators who spend more time covering up the sources of election spending on their behalf than they do legislating? How can we trust a candidate who won’t be open and honest with voters about the source of his personal fortune and the taxes he has paid?

Full disclosure should be a no-brainer in honest politics. The public knows that. Even the Supreme Court knows that. The only people who seem to be missing the message are the politicians who are desperately trying to win elections without telling voters who might be buying them.