Perhaps the Greek government's biggest misjudgment since it was elected in January has been to assume that the solution to its debt crisis lies in Berlin, or Brussels, or Frankfurt. It has spent much of its first three months trying to browbeat European governments and the European Central Bank into handing it condition-free money. Last week, the action shifted to where Athens's attention should always have been focused: Washington, D.C. The key to any Greek debt deal lies with the International Monetary Fund.

The IMF was brought into the eurozone bailout programs from the very start in 2010 because its expertise, rigor and independence were seen as crucial to persuade skeptical European parliaments to stump up taxpayer cash for crisis-stricken countries. That decision was controversial--many believed Europe should have been able to deal with its own problems. But once the IMF came into the process, it became politically indispensable: no IMF, no deal.

Berlin has been hiding behind the IMF throughout the current crisis. Ask German officials to defend previous Greek bailout programs and they will reply that it wasn't they who designed them but the IMF; ask what conditions Athens needs to meet to receive bailout funds and they will reply that is a matter for Greece and the IMF. The message from Berlin is that only the IMF has the technical skills to analyze the fiscal impact of Greece's reform plans; a deal that is good enough for the IMF is good enough for Berlin.

This has put the IMF in an invidious position. The IMF is trusted because it has rules and procedures designed to shield it from the kind of political interference that has undermined confidence in European institutions, the European Commission in particular.

The IMF draws its funding from 188 members, among them many of the world's poorest countries, and is only supposed to lend where it is confident that the debt burden is likely to be sustainable and that the borrower is likely to have access to market funding when the program ends. These safeguards explain why the IMF is seen as the world's safest lender.

But the IMF also prides itself on being a source of global financial stability and certainly not a source of instability. That can make life complicated when dealing with a member of a currency union such as Greece.

In 2010, the IMF agreed to the first Greek bailout program despite deep misgivings on its board and among its executives that the debt wasn't sustainable because it feared that any restructuring of Greek debt could destabilize the whole eurozone. Critics argue that the extra debt and austerity demanded of Greece instead were a major reason for the scale of the economic collapse.

Now the IMF finds itself in a similar bind. It has loaned money to Greece on the basis of a detailed memorandum of understanding, a legally binding contract that sets out the reforms Athens must undertake to receive IMF cash.

For almost a year, the IMF has been refusing to pay the next bailout installment to Greece until it completes the reforms required under that deal. It stuck to its guns even as the previous Greek government fell and the new one has come close to bankruptcy.

Those reforms were reiterated in a letter in February from IMF Managing Director Christine Lagarde to Eurogroup President Jeroen Dijsselbloem: They included reform of the Greek pension system, labor market, product and services markets, the tax system and public administration.

But the IMF appears to have blinked. Although its agreement with Greece is separate to that of the eurozone's, the IMF has had to recognize that for practical purposes they are the same: The eurozone has boxed itself in and won't distribute its funds even to alleviate an acute liquidity squeeze until Greece has reached a deal with the IMF. The IMF's intransigence risked pushing Greece toward a messy default and possible euro exit that no one wanted. So the IMF last week agreed to streamline its demands.

This is a significant move. Greece must still agree on and implement difficult reforms, most likely including some overhauls of pensions and value-added tax. And some officials fear that even a streamlined deal may prove too much for Athens to deliver before a mid-May deadline when parliamentary approvals must begin if cash is to be disbursed before the program expires at the end of June. But the IMF has lowered the bar to a Greek deal.

Even so, it will still need to satisfy its shareholders that Greek debt is sustainable before it can deliver its cash. That could be tricky: The combination of a reduced reform program and the impact of months of political turmoil on Greece's growth prospects will have opened a large funding gap. Greece's debt burden will need substantial restructuring, something eurozone governments have ruled out beyond changes to interest rates and maturities on existing loans.

Much may then hinge on how rigorously the IMF decides to enforce its own debt-sustainability rules. Will it demand that the eurozone play its part in resolving the crisis, with the risk that it refuses, leaving Greece unable to pay its debts? Or will it bow to eurozone political reality and fudge its analysis again, as it did in 2010, thereby ensuring Greece's drama drags on? All eyes should be on Washington.