Kudos to Maggie McKinley, Climenko Fellow and former Lab Fellow, and to Network Fellow Thomas Groll for an impressive blogpost. They argue in a mixed-methods design—drawing on both qualitative data and formal analysis—that much of what lobbyists do isn't really quid pro quo corruption, notwithstanding the appearances. A couple of thoughts to extend the conversation:
First, just to define terms, quid pro quo (QPQ) corruption is the exchange of "this for that," done with a corrupt intent, or in short: bribery. According to the current doctrine about the law of bribery, and common sense, quid pro quo agreements can exist, even without an explicitly-stated agreement between the parties.
McKinley and Groll observe that lobbyists bring lots of things of value to Members of Congress, including campaign funding (directly and indirectly), and the Members of Congress provide many benefits to lobbyists, including the very policy outcomes that the lobbyists are paid to produce. Indeed, McKinley and Gross cite McKinley's data finding that "lobbyist participants would often remind lawmaker offices of other forms of electoral support provided by clients when discussing a client issue or setting up a meeting." Thus, we see this linkage, making the “quids” salient to decisions about “quos.” Nonetheless, McKinley and Groll conclude that it is (usually) not a matter of quid pro quo corruption. Instead, they suggest that it may be the broader sense of "institutional corruption," one that is well known to readers of this blog.
How can researchers rule out QPQ? Obviously, we can't simply ask the parties to the alleged transaction.
To help rule out QPQ, McKinley and Groll invoke the often-said argument that the campaign money paid/spent by lobbyists can't be quid pro quo bribery, because the amounts (quids) are too small in comparison to the potential benefits (quos) that the policymaker can deliver. If we knew that paradigmatic cases of bribery are proportional, and if the quids and quos typical of lobbying relationships could be quantified and found disproportional, then one could distinguish lobbying transactions as atypical of bribes. (Even then, it would be a weak, gestalt sort of evidence, since these could just be a different species of bribe.)
So there are empirical claims here. Anecdotally, I am aware of proven/admitted cases of bribery, where judges and commentators point to such a disparity to emphasize the venality of the policymaker. For example, in Duke Cunningham's famous case, he actually offered a bribery menu, exchanging $50,000 quids for each $1,000,000 in quos. That's a nice 20:1 return on investment (ROI). More systematically, scholars have studied empirically whether quids and quos are typically proportional in bribery cases, and found that a 14:1 ratio is typical in the U.S. Thus, the major premise of the disproportionality thesis seems false: paradigmatic bribes are not necessarily proportional.
Still, it is helpful to understand why quids and quos could be exchanged without proportionality. One factor is that the policymaker may be personally nearly indifferent between policy A and policy B. Her marginal cost of producing policy B (uttering "yay" versus "nay" on the day of the vote) is essentially zero. Thus, subjectively in the eyes of the official, the deal may seem more proportional than it appears from the outside. On top of this, larger quids likely draw a greater risk of enforcement, and a greater sense of cognitive dissonance for everyone involved. Furthermore, in terms of market power, it may also be that policy incumbents face more churn than market incumbents. Finally, for direct contributions, of course, we also have price controls ($5,200 per cycle). For all of these reasons, it may be sensible to settle on an equilibrium with relatively small quids, even for highly valuable quos.
These sorts of market dynamics can make quid pro quo transactions rational, even if the transaction doesn't split the pie evenly between the two parties. Consider another context—lobbying itself. Of course it is indisputably a quid pro quo relationship—companies pay lobbyists for specified services, based on explicit contracts, periodic invoices, etc. Prior research has shown that lobbying has an enormous return on investment (e.g., 22,000%). Why don't lobbyists charge more, to capture more of the bargaining surplus they are creating? I don't know. But the crazy ROI doesn't cause me to doubt that lobbyists are engaged in a quid pro quo relationship with their clients. Similarly, if we are worried about corruption of politicians, we shouldn't let a huge ROI cause us to doubt that it is a quid pro quo relationship. It may or may not be QPQ, but this factor seems unimportant in making that determination.
So, I'd suggest that we put this proportionality argument to rest. McKinley and Groll offer several other arguments, however, which help advance our understanding of these problems, and may distinguish quid pro quo corruption from institutional corruption. I'm eager to see the underlying research. Their work has already caused me to delve deeper in these paramount questions.