Hillary Clinton has flipped Sanders' claim around and challenged him to show where she has reversed a position to serve the moneyed interests. This might be a useful campaign tactic, but it misrepresents the way in which money affects campaigns.

Undoubtedly there are cases where an individual or industry group promises a large campaign contribution in exchange for a politician's support on a particular issue, but this is almost certainly rare. More typically the support of politicians for moneyed interests is part of a much longer process. It's not just that the politician wants to act to curry the favor of the rich and powerful, more typically they identify with the interests of the rich and powerful so that they don't even see themselves as compromising a principle.

Trade policy provides an excellent example. During the last quarter century, the leadership of both political parties has consistently pushed trade deals that have worked against the interest of a large percentage of US workers. This was not an accidental outcome from these deals, it was by design.

Trade deals like the North American Free Trade Agreement (NAFTA) or most favored nation trade status for China were designed to put manufacturing workers in the United States in direct competition with low-paid workers in the developing world. According to standard trade theory, the predicted outcome of this competition is a loss of jobs in manufacturing and downward pressure, not only on the wages of manufacturing workers, but on the wages of less-educated workers more generally.

The wages of other workers would fall since displaced manufacturing workers would be forced to look for jobs in retail and other sectors. The increased supply of workers lowers wages in these other sectors as well. Recent research by some of the country's top labor economists confirms that trade has been a major factor depressing the wages of large numbers of workers.

While there were big money beneficiaries of these trade deals, most of the politicians who supported them probably did not need to be bought with campaign contributions. Instead, they likely supported these deals because they thought they were the right thing to do. After all, they mostly associate with people who benefit from these trade deals, either through higher corporate profits or from being able to buy cheaper cars and clothes. Politicians are less likely to associate with the auto workers or textile workers who were losing jobs or retail clerks getting lower pay.

In most cases, it probably never even occurred to the politicians voting for the pacts that there was a serious downside. Politicians are people who get elected by making friends and raising money, not by being policy wonks or political philosophers. Being an expert on the issues that Congress or the president addresses is not part of the job description.

Furthermore, even if they looked beyond their friends they could find media outlets like The Washington Post touting the virtues of "free trade." Never mind that these deals did nothing to reduce the barriers that protected highly paid professionals like doctors or lawyers or that they actually increased patent protection on drugs and other products. Since these forms of protectionism benefitted the wealthy, the deals could still be called "free trade" pacts.