As illustrated by the current budget standoff, an unpopular lame duck president has powers that often elude presidents earlier in their tenure. Prior to 2006 Bush never vetoed anything. Now he has no re-election to worry about so he has nothing to lose by vetoing every bill Congress sends that is not in line with what he wants. Eventually they have to override the veto or fall in line with his request.
Because his popularity is already low he does not have to worry about disappointing anyone by sticking to his favored position. By standing firm he takes the chance of raising his popularity. If that fails the other members of his party are already prepared to keep their distance from him. The odds are highly against this coming out good for the Democrats.