Assistant editor and Opinions contributor

Former Virginia governor Robert F. McDonnell (R) leaves the Supreme Court on April 27. (Alex Wong/Getty Images)

Over the past couple of years, former Virginia governor Robert F. McDonnell has been surrounded by a media circus thanks to his potential prison sentence for corruption charges. But the Republican may yet find his saving grace in the Supreme Court whose members, during arguments last week, seemed ready to dismiss his charges — accepting cash and gifts for greater access to his office — as just politics.

The case comes at a perfect time: an election year in which candidates have been throwing around the word “corrupt” on a seemingly daily basis. But the case does highlight a politically loaded question: What exactly is corruption?

Political scientists have identified three variants of the concept emerging from the legal world: quid pro quo corruption, monetary influence and distortion.

Quid pro quo focuses on the “you scratch my back, I scratch yours” bribery deals that occur between donors and politicians. Under this legal concept, corruption only exists if there’s been a clear transaction, such as exchanging money or a gift for a vote. This is meant to protect political speech. If you like a candidate, you have every right to support him or her in any way — free from fears that some day the legal system will prosecute you for having close relationships with those in power. That is to say, you can spend as much money as you want on ads promoting your preferred candidate so long as there are no favors attached. You can also give gifts, donate plane rides or let politicians use your summer vacation house — all assuming that doing so doesn’t come with expectations for legislative perks down the line.

It’s the “perks” part of the equation that’s put McDonnell in hot water over the past couple of years. After receiving many gifts from Jonnie R. Williams Sr., owner of a dietary supplement company, McDonnell responded by hosting luncheons and granting meetings with the businessman. Free speech advocates have supported McDonnell, arguing that he never delivered any “official act” in exchange for favors and therefore didn’t fulfill any sort of corrupt transaction. Sure, the governor gave Williams greater access to his office, but was that corrupt under the law?

The Supreme Court under Chief Justice John G. Roberts Jr. has placed a strong emphasis on quid pro quo corruption over the past few years, and for many proponents of campaign finance reform, the McDonnell case is emblematic of how the wealthy and powerful have an unfair say in politics. But those proponents also want to go further, identifying the simple presence of monetary influence in government as a version of corruption. It would be corrupt, for example, for a rich chief executive to spend a bunch of money on ads supporting a politician, creating a sort of political debt. This is often referred to as “rent-seeking.”

For example, critics harshly condemned Wisconsin Gov. Scott Walker (R) as corrupt when it was revealed that a mining company — which the state permitted to begin iron mining in Northern Wisconsin after the governor’s 2012 recall election — secretly donated $700,000 to pro-Walker conservative groups during the election. Walker said he had no knowledge of the donation, and the investigations have since been ended. Still, the ordeal left a bad taste in the mouth of opponents, who claim Walker is controlled by industrial powers. Critics of monetary influence argue that the solution to this sort of corruption is fairly straightforward: Overturn the 2010 Citizens United decision that allowed corporations to spend unlimited amounts of money independent from political campaigns.

And still, many others want to go even further, suggesting that policy should strictly reflect the views of the public and never those of special interests. Under this popular view, the immense wealth of some individuals inherently distorts policy decisions and corrupts the political system. This is the logic that underpins popular frustration with, say, liberal George Soros or the conservative Koch brothers — billionaires who have built massive networks of donors and advocates.

In fact, for the current election cycle, close to half of all super PAC money has come from only 50 donors. For many of their critics, powerful business advocates are corrupt not because they are directly benefiting from under-the-table deals with politicians, but simply because they have a lot of influence over party agenda. This subverts the democratic process and undermines the concept of “one person, one vote.” The solution is not only to limit the amount of contributions that corporations or wealthy individuals spend on campaigns, but to break up their power bases through government action. The prime example: Bernie Sanders’s call to “break up the banks.”

Each flavor of corruption is neatly featured in this campaign season. Ted Cruz has long held campaign finance reform as an “assault on free speech.” Hillary Clinton wants to overturn Citizens United but doesn’t think money from private groups (including her speaking fees from Goldman Sachs) corrupts politicians. And both Sanders and Donald Trump condemn the distortion of the political system by powerful people and promise to overthrow the whole system if elected. (Meanwhile, John Kasich supports whatever system will let him win).

The debate really comes down to a tug of war between political equality and free speech. How much influence should one person’s voice have over another’s? What role should our legal system play in protecting political equality, and how can it do that best?

Over the next few days, we’ll hear from:

Trevor Burrus, senior fellow at Cato Institute

Jacob Rowbottom, professor of law at Oxford University

Stephen K. Medvic, professor of government at Franklin & Marshall College

Zephyr Teachout, professor at Fordham Law

Daniel Treisman, comparative politics professor at University of California, Los Angeles

Nancy Gertner, former federal judge and Harvard lecturer