There seems to be some indication that they hired some incompetent people and/or were prohibited from cutting some of the things that ought to be cut. And I don't think there is any question that the deadline they set for themselves was unrealistically aggressive.
Which means we need someone to go back and do it properly, not that it doesn't need to be done.
Sure it can, by the atorneys general. A core part of their job is identifying, stopping, and prosecuting fraud and waste spending in the government.
Doge was never legal, but there were agencies that had the statutory power to do what doge wanted. However, they also could investigate things like emoluments violations which is precisely why they were some of the first to be fired.
Which means we need someone to go back and do it properly, not that it doesn't need to be done.