LONDON — By defying Washington and delaying his signature on the bilateral security agreement with the United States to continue financial and military aid for Afghanistan after 2014, President Hamid Karzai is being both very astute and supremely foolish — astute in a personal and Afghan context, foolish in an American one.

Mr. Karzai is clearly trying to garner nationalist support, especially among his fellow Pashtuns. He may also hope that withholding his signature may give him some leverage over Washington during next April’s Afghan presidential elections — which he may well need, since these elections are extremely unlikely to proceed according to strict Western democratic rules. Mr. Karzai’s own desired future as a powerful figure in Afghanistan depends on this, but he may also genuinely believe that an ability to manage these elections peacefully (rather than democratically) is crucial to preserving the Afghan state.

Unfortunately, United States support is also crucial to Afghanistan’s future. The key issue is not American bases, but money. At present, barely one tenth of the Afghan budget is paid for by Afghan revenues, and there is no realistic chance of quickly increasing those revenues. Virtually the entire military and development budgets are paid for through American and Western aid. Washington has insisted that a deal that would allow for an American troop presence through 2024 and sets the stage for billions of dollars in international aid needs to be signed by the end of this year.

This is where Mr. Karzai’s maneuvering is so dangerous for Afghanistan. For he does not appear to recognize the depth of the desire in Washington and European capitals to be quit of the whole Afghan morass. Mr. Karzai is therefore playing Russian roulette with a pistol pointed at his country’s head, and may not even realize how many of its chambers are loaded.