The Washington Post offers an instructive campaign finance story this morning. The essence of the story: employees of banks and brokerage houses contributed more to candidate Barack Obama in 2008 than to his rival John McCain. A lot more in fact: such employees gave almost twice as much to the current president at they did to the Arizona senator.

Now, however, President Obama is attacking the banks and Wall Street for greed and selfishness, not to mention for ruining the economy. Moreover, Obama is proposing curbs on Wall Street pay and heavy regulation of banks. It would appear, in other words, that contributions don’t buy many favors with this administration.

But the story goes deeper. Wall Street is now shifting its contributions to the GOP. That’s not surprising. In fact, being an intelligent man, President Obama must have known his attacks on Wall Street might deprive his party of contributions. Yet, he went forward with the attacks and proposed laws.

Why? In the coming election, contributions will matter a lot less than votes. Obama thinks his attacks on Wall Street will cast the Democrats as the party of “us” against the detested “them.” The votes gained will greatly outweigh the donations lost. The currency of politics is votes in the market for election.

The next time someone tells you that donations are “legalized bribery,” ask them why Obama took $18 million from Wall Street and gave them in return endless abuse and hostile legislation.

Quid pro quo, indeed.