Two-thirds of the $50 million spent on Mitt Romney’s behalf in Ohio has come from outside “super PACs” and other so-called independent groups, and yet Mr. Romney has lagged behind in all of the major Ohio polls. Hundreds of millions in third-party spending from unlimited checks, much of it from undisclosed donors, has also failed to give Mr. Romney a clear lead in any of the other swing states.

If Mr. Romney loses the presidential race — which is far from a sure thing — does that mean the big check writers will declare the process a waste of money and stay out of politics the next time around? Don’t count on it.

This is only the first presidential election in the Citizens United era of unlimited spending, and the first since 1976 in which both presidential candidates spurned the public finance system. All the big players are learning lessons about how the process works in an ugly new world, and will be fine-tuning their strategies once they determine what was effective and what was not.

There may be some changes in how unlimited money is spent, but now that it has been unleashed, only a constitutional amendment or a careful system of regulation can bottle it back up. The need to do so will remain one of the most urgent challenges facing every lawmaker.