Politicians and bureaucrats care very little about unregulated securities, as evidenced by the fact that very few shitcoins have been shutdown. The regulations that they are enforcing cover all cryptocurrencies equally (e.g. KYC/AML). So, if Congress tightens cryptocurrency regulations, Bitcoin will be affected just as much as shitcoins.

That being said, there's a small chance that a ton of shitcoins will be wiped out by the market before Congress gets around to passing strict cryptocurrency laws.