Make sure Detroit pays us back—buy their cars.

Imagine you're an elderly parent with a couple of deadbeat, middle-aged children. Your kids—who we'll call Germane and Chrys—have their own auto-repair shop, which has recently fallen on hard times of its own making. Their methods were outdated, their service and products were lackluster, and they got pushed out by the competition. But they're too integral personally and financially to your family to let them become poor louts. So you float them a loan and hope they can get back on their feet. Of course, you had to take out a loan yourself for that money, so you'd prefer to get the money back.

Next time you need your car fixed, where are you going to take it? To the better mechanic who you know will get the job done? Or to the shoddy but improving mechanic who will be able to pay back the loan only once business improves? It's in your financial self-interest to swallow your pride and drive business to your deadbeat kids.

I offer that transparent metaphor to show the trickiness that we've gotten ourselves into with GM and Chrysler. Dismal auto-sales numbers released Monday confirmed that the situation isn't getting better on its own. Overall, sales of cars and light trucks dropped 36 percent in December. GM was down 32 percent. Chrysler down 53 percent. Unfortunately, the two companies are all of our responsibilities now. And if we ever want them to pay us back, we better start buying their cars. Consider it your patriotic duty.

When we finally bailed out the auto industry, we actually just offered loans to two of Detroit's Big Three. (Ford declined assistance.) GM received $9.4 billion, and Chrysler took $4 billion, with more money likely to come. I'm using the term we intentionally, since the money is coming from public dollars that are funded by Americans' taxes. Assuming you aren't Wesley Snipes, you have as much of a stake in the car companies' futures as anybody else. We're all in this together.

(You can see the loan term sheets here and here, but I warn you that they're written in a strange dialect that combines corporate-speak with legalese. Like Latin, it is only written, never spoken, and people go to school to study how best to write it.)

In exchange for the loans, we were guaranteed up to a 20 percent stake in the companies, should we choose to take that option. If we lend more money down the line, we could potentially have rights to a larger stake. Whether or not the government takes ownership in that 20 percent, we have an incentive to see the companies do well. If we own part of the companies, then we'd like to see the stock go up so we can sell our stake for more than we bought it. If we have only extended the loan, then we'd like to see it get repaid so that we don't have to deal with a $13.4 billion-plus hole in the budget a few years from now.