The mortgage rescue plan is simple on paper: it gives the US Treasury a large chunk of money and a lot of discretion about how to spend it. But it is likely to turn out to be much more complex to execute.

The plan gives the Treasury something close to a $700bn blank cheque to buy troubled assets from financial institutions and either sell them on or hold them until they mature. It will have wide discretion about which assets to buy and for what prices, and what to do with them afterwards.