I’ll get to the existing homes sales report in just a bit, but, before doing so, I wanted to point readers to this commentary by Jonathon Weil at Bloomberg today that points out one of the most disturbing aspects related to the nexus of politics and finance today – the ongoing partisan divide over what caused the financial crisis a few years back.

The way the discussion gets framed tends to go like this: Did Fannie and Freddie cause the crisis? Although this is the wrong question, I’ll try to answer it anyway by highlighting the difference between the meaning of the words “a” and “the.”

Here goes. Fannie Mae was a cause of the financial crisis. So was Freddie Mac. U.S. government housing policies, which often encouraged people to take out loans they couldn’t repay to buy homes they couldn’t afford, were also a cause. None of these was “the” cause of the crisis, because there was no single cause.

Two people often cited as proponents of the notion that Fannie and Freddie caused the crisis are Peter Wallison and Edward Pinto. Both are fellows at the American Enterprise Institute, a Washington think tank. Wallison was a Republican member of the Financial Crisis Inquiry Commission who wrote a 98-page dissent to the panel’s final report in 2011.

Last month, in an article responding to a column by Joe Nocera of the New York Times, Wallison and Pinto framed their thesis this way: “Our argument is and has been that the financial crisis would not have occurred but for government housing policy implemented principally through Fannie and Freddie and the Department of Housing and Urban Development.”

It’s a debatable, if not a particularly useful, observation. One reason Wallison and Pinto have drawn so much criticism for their work is that they consistently dismiss every other possible cause of the crisis, so that only Fannie, Freddie and U.S. housing policies survive the scholars’ own “but for” test. Never mind interest rates held too low for too long, worthless regulators or banks with excessive leverage, for instance.

Even New York Mayor Bloomberg came down in the “the cause” camp a month or so ago when referring to the role the government played in the housing bubble. It’s simply amazing to me that so many people seem to insist on viewing this as a black-and-white issue – that either Washington or Wall Street are to blame, but not a combination of the two.