That’s more or less what the Congress gave the Secretary of the Treasury (Paulson, under President Bush), in order to save the economy when it was threatening to crash and burn in the fall of 2008. Here’s the Text of Draft Proposal for Bailout Plan (NYTimes.com).
Basically it gives Paulson the ability to buy any mortgate-related asset from anyone for any amount up to $700B. It’s a remarkable document. Read it just to see how much leeway Paulson had. It’s astounding.