WHEN IT COMES to the corrosive influence of money in politics, the 2012 campaign has presented a trifecta of troubling developments. They are, in ascending order of worry: the complete collapse of the presidential public financing system set up in the wake of Watergate; the explosion of the super PAC political committees, which are allowed to take unlimited checks to finance independent expenditures for or against particular candidates; and the proliferation of “dark money,” or spending by nonprofit organizations and trade groups that, unlike super PACs, are excused from having to reveal their donors. The end result is a system awash in cash and dangerously ripe for corruption.

Every presidential cycle ends up costing more than the last, but 2012 marked the first presidential election since Watergate to be underwritten entirely by private money. This development left the candidates spending even more time than usual scrambling for dollars and beholden to the bundlers who rake in hundreds of thousands, if not millions, in donations. Along with their allied parties, each candidate raised more than $1 billion. President Obama, who helped break the system and then ignored his pledge to try to fix it, at least discloses the identity of his bundlers. Mitt Romney, unlike his two Republican predecessors, has refused even that minimal transparency.

The most dramatic development of the 2012 campaign has been the explosion of super PACs and the emergence of candidate-specific super PACs as a major force in the presidential campaign and, in some cases, congressional races.

According to the Center for Responsive Politics, super PACs have spent more than $600 million this election, mostly underwritten by huge checks from wealthy donors. The biggest known givers have been Las Vegas casino magnate Sheldon Adelson and his wife, Miriam, who together have contributed $53 million to Republican causes, including $20 million to Restore Our Future, the super PAC backing Mr. Romney. Run by Mr. Romney’s former aides and advisers, Restore Our Future has spent more than $138 million during the primary and general election campaigns. Priorities USA Action, the super PAC supporting Mr. Obama and run by his former aides, has spent $68 million attacking Mr. Romney. To put those number in some perspective, four years ago Republican nominee John McCain received $84 million in federal funding for his entire general election campaign.

None of this is healthy. Outsized contributions by a wealthy few threaten to distort the political system. Secret contributions threaten to corrupt it. In light of wrongheaded rulings by the Supreme Court, these problems will be difficult to fix. But at the very least, ramped-up disclosure rules and limits on what super PACs can do in coordination with particular candidates would improve a system in critical condition.

Even more troubling was the surge in 2012 of “dark money” spending by outside groups — supposed nonprofit “social welfare organizations” and trade associations — that take advantage of permissive interpretations by the Federal Election Commission and Internal Revenue Service to avoid disclosing donors. The Center for Responsive Politics reports close to $300 million in such secret money.