What's kept the administration from being as bold as its critics want is not a lack of imagination, or a lack of contact with the outside world, or an overreliance on the banks....It's a combination of the knowledge that Obama cannot do big things unless he remains a majority president, that he could make a hash of them if Congress perceives that the administration is pushing too close to the boundary of what's acceptable, and that the administration has accepted that it cannot allow Congress to be a partner in leading the American people towards a solution. The stimulus package debate in February was dispositive; the administration lost confidence in Congress's maturity fairly quickly.
It's not clear how much of this is just Ambinder's own judgment and how much is informed by his reporting, but presumably he wouldn't say this if he didn't have good reason to believe it. And that's pretty interesting: Obama no longer trusts Congress. It's also a wee bit frightening, no?
(Ambinder also has a list of questions he thinks need to be answered before any kind of nationalization plan is possible. I don't quite understand some of them — why would there be a run on a nationalized bank? — but they're worth taking a look at.)