We’re talking about the government here, it’s entirely reasonable to assume they’re going to start regulating this kind of thing by imposing rules on citizens.
How are they going to regulate defi?
The most likely thing is to add onerous reporting rules on US citizens since they can’t directly change any of these protocols. Or, declare that participating in DeFi without a license is illegal. Again, they can’t ban DeFi because it’s decentralized but they can certainly regulate you and I’s interaction with said systems.