Most of what I read about Musk is frankly too angry to be persuasive. This doesn't talk a lot about Musk specifically, but it is a look at past efforts at government right-sizing and the perils therein, which might be useful? https://www.npr.org/2025/03/12/1237991516/planet-money-doge-government-size-rego

And here's a piece specifically about IRS cuts: https://www.propublica.org/article/how-doge-irs-cuts-will-cost-more-than-savings-trump-musk-deficit

Edited to add, again, this piece from Atlantic, although I'm not sure she'll find it persuasive (and you'll need to use a proxy to get through the paywall if you don't have an account): https://www.theatlantic.com/ideas/archive/2025/03/doge-deficit-trump-elon/682227/

And here's some Social Security-specific reporting: https://www.washingtonpost.com/business/2025/03/24/social-security-fraud-doge-cuts-dead/
https://www.cbpp.org/research/social-security/trump-administration-doge-activities-risk-ssa-operations-and-security-of