Yesterday, Harvard historian Niall Ferguson told Bloomberg viewers that there is no way Greece will be able to pay its debt. “It is 100 percent certain that Greece will default—the only question is what euphemism will be dreamed up to cloak the fact that it’s in default, and the race is on to find a way to say that Greece really hasn’t defaulted even though it’s not making good on its interest payments.”

But if a debt default is inevitable, just who will be stuck with the loss when Greece stops paying? Most people have assumed that it would be the big German, French and British banks that lent Greece the money it can no longer afford to pay back.

However, a recent report from analyst Kash Mansori at The Street Light blog shows who will really end up picking up the tab for Greece’s recklessness—and if you pay taxes in America, it isn’t good news. Using data from the Bank for International Settlements, Mansori sorts through who has loaned Greece money—and just as importantly, which banks have insured those loans.

Guess who is the major insurer of Greek loans? You guessed it: American banks. Those same “too big to fail” banks bailed out by taxpayers three years ago.

Here is how it happened. French and German banks lent Greece money. Normally, if Greece stopped paying, the French and German banks would take the loss. Case closed.

However, over the past few decades, American banks pioneered the use of new financial products called derivatives. One type of derivative is known as a credit default swap. You can think of it as insurance. American banks sold tens of billions of dollars’ worth of default insurance to those lending money to Greece (and to Ireland, Portugal, Spain, Italy and so on).

But here is the catch. For many of the years that American banks were selling default insurance against a Greece default, Greek finances appeared healthy. Plus, as it was later revealed, other big American banks like Goldman Sachs were using different complex “derivative”-like products to help Greece hide the true state of its finances. The upshot of it all is that American mega banks sold their default insurance way too cheaply. They were too smart for their own good and vastly underestimated the chances of default.

Consequently, if Greece does stop paying its bills, American banks are going to have to cough up billions—and because of the 2008 economic collapse, they just don’t have that kind of money.

The “too big to fail” are back.

According to Mansori, if Greece defaults, American banks will be responsible for reimbursing German, French and other lenders $41.4 billion. If Portugal collapses, American banks would be forced to pay up an additional $46.5 billion. And if Ireland goes bad, they would need to find a further $105 billion.

In dollar terms, American banks are just as exposed to a European meltdown as the Europeans are, says Mansori. “[O]nce you account for the substantial payouts that U.S. agents will have to make to European creditors in the case of a default … financial institutions in the U.S. have roughly as much to lose from default as those in France and Germany.”

Making the situation all the more dangerous is that nobody knows just how exposed individual American banks are. Who is solvent and who isn’t? It is the stuff of credit crunches and crises.

“When, not if, Greece defaults, U.S. banks are going to have to dip into capital to pay those commitments,” says economic analyst John Mauldin. “Capital that should be available for loans to businesses but will have to be paid to European banks instead.”

“Why, oh why, are banks putting American taxpayers at risk, as these too-big-to-fail banks certainly are?” he wrote in his latest Thoughts From the Frontline post. “And make no mistake, if several major banks were to collapse, our government would need to step in. The largest banks are too big for the fdic to handle. Now, shareholders would be wiped out this time and bondholders would face haircuts. No question.”

Economic catastrophe 2008 could soon be back with a vengeance.

Think it is hard to get a loan now? Think jobs are scarce? Worse could easily be coming.

Plus there is a growing realization in Europe that bailouts are fraught with political risk. According to Ferguson, there is a massive battle raging between Germany and the European Central Bank. The ecb wants to keep bailing out Greece in order to prevent an actual default. However, Germany, which is the country that would end up paying the majority of the bailout, wants investors who chose to lend Greece money to take the majority of the losses. German voters are increasingly upset that their tax dollars are bailing out big-spending countries. If German taxpayers are to pick up the tab, then German politicians say bailed-out nations need to give up control over their budgets and powers like taxation.

For now, the ball seems to be in Germany’s court. If it opts for more bailouts, American banks might be spared for a while. And Germany will further consolidate its economic grip on the Continent. But if Germany decides to let Greece fail, a second major banking crisis could easily erupt.

Watch Greece—but more importantly, watch Germany.