U.S. politicians vote to spend money, and then separately vote to authorize borrowing money to fund that spending. Both Republicans and Democrats favor raising the ‘debt limit’ but Republicans want Democrats to have to say how much they favor borrowing to fund their spending plans, since Democrats currently control both houses of Congress and the Presidency.

That’s why Republicans haven’t been willing to raise the debt limit as a part of funding the government and avoiding a shutdown. They want Democrats to pass the debt limit as part of ‘reconciliation’ which would let them do it on a party line vote but would require them to name a number rather than just extending it to a specific point in the future.

In the midst of this political skirmish the idea has once again surfaced to have the Treasury mint a trillion dollar coin and deposit it at the Fed in order to avoid the need to borrow more money. So it’s worth remembering just where this idea originateed: one of the best frequent flyer miles deals.

• The Wall Street Journal‘s Scott McCartney learned about the old miles bonanza of buying dollar coins from the US Mint with a credit card (with free shipping) and depositing those coins into the bank when he attended a frequent flyer event. He wrote about the technique in the journal.

• That’s where lawyers and monetary policy experts saw it. And the idea of buying coins and just depositing them inspired the idea of a similar scheme with the Treasury and Fed.

I first wrote about buying coins from the U.S. Mint in June 2008. In the summer of 2009, the deal exploded as the Mint lifted the per-person cap on purchases.

After attention in the press, the Mint took some heat for letting the practice continue. And they started to scold some people for doing it in some pretty extreme ways.  But the deal continued on, it wasn’t actually killed at that time.

By the summer of 2010, the mint placed a limit of $1000 in purchases every 10 days.  But, of course, people continue to purchase what they were willing to sell. Some credit card programs, like US Bank Flexperks, stopped awarding points for the purchases. And Chase closed down accounts from some very high volume purchasers. But on the whole, things were still chugging along fine, even a couple of years after the deal had gotten public scrutiny. NPR covered it, highlighting that this deal was still alive, in mid-2011. And then it finally died.

In my own view the trillion dollar coin is a bad idea because of legal uncertainty. The time challenges would take to work through the courts would be terrible for markets and banking.

The really important question, though, is this: If the Treasury mints a trillion dollar coin, can I pay for it with a credit card? And, crucially, will my card issuer treat it as a cash advance?