The Democrats absolutely need the Republicans to be in on this. Without the Republicans, the Democrats would take all the heat on this highly unpopular bailout, and they would get killed in the congressional elections.
For that reason, the Republicans are in the driver's seat here, and they can demand anything they want.
And if nothing gets done, the Republicans (and McCain if he stays with them) still come out on top for stopping this monstrosity.
McCain can’t support the Frank/Dodd/Pelosi version without losing his cred as fighting spending.