Shortly after the election, Bush said, "I've earned political capital in this election, and I'm going to spend it."

An interesting metaphor, one which suggests a politician's power is like a bank account where he can save up his influence or choose to consume it to get some agenda passed. Bush was clearly indicating he planned to take the latter course.

But how apt is this power-as-bank-account metaphor?

Earning Political Capital
To begin, we need to define what Political Capital (or PC for short) is. PC is the ability to influence the outcome of political events. As such, it is basically the perception of a politician's power.

Elected offices come with a certain amount of inherent PC, through the ability to vote on (or veto) legislation. A politician earns more PC in one basic way: by winning. Winning an election always earns PC, since it shows that a plurality of the voters in the politician's district back him or her. Plus, it means that the politician will be sticking around for another two, four, or six years. In contrast, losing an election wipes out all PC, for obvious reasons.

PC can also be earned by winning important (and especially controversial) votes in the legislature. If a politician pushes an issue hard (like Social Security reform) and wins, that increases his or her perceived power, and hence earns PC. In this case, spending PC can actually earn PC--but at a risk. If the politician loses, then the PC is gone forever, as losing an important vote decreases his perceived power (this is sometimes called "overreaching").

Finally, PC can be traded, but not in the usual sense. Since a successful trade can help both sides advance their agendas, trading PC can actually increase the total PC for both sides. People who don't hold political office (lobbyists, for example) can earn PC through trading with politicians. People who are especially good at trading PC are often called "power brokers."

Spending Political Capital
A politician spends Political Capital to influence the outcome of political events. This takes the form of trying to convince other politicians to vote in a particular way.

For example, a newly-reelected President may spend his PC by arguing to a Senator that it would be foolish to vote against the will of the voters. Or one congressman might offer to trade a vote on a particular bill for a vote on a different bill.

In all cases, when a politician spends PC, it isn't necessarily gone. If the outcome is what the politician wanted, that may actually increase his PC, since everyone will perceive him as being more powerful as a result. On the other hand, if the politician loses, the spent PC is gone for good.

In this respect, the power-as-bank-account metaphor breaks down. A better metaphor might be power-as-poker-chips: one way to get more PC is to risk it, and if you win, you get more.

Saving Political Capital
Unlike real capital, you can't really save Political Capital. If you've got it and don't use (or trade) it, it goes away.

This isn't to say that a politician has to be engaged on every single issue, but that power which is never used is really no power at all. PC certainly doesn't earn interest the way a bank account does.

So really, PC isn't that much like a bank account after all. But as a rhetorical device, it turns out to be a great hook into writing a long article.