The Samurai wallet indictment alleges the Samurai service is a money transmitter despite not meeting the definitions set forth by FinCEN. The service itself never took control of funds nor did it transmit the funds. If this case rules in favor of the DoJ then it sets a precedent that could be used to target mining in the US.
A miner takes transactions and includes them in a block and then broadcasts them out to the network. This process is not meaningfully different from what Samurai was doing if we go by the extremely loose definition of money transmitter the DoJ is proposing.
This means that all miners could eventually be forced to apply for a money transmitter license which can be denied or revoked on political grounds. It also drastically raises the barrier of entry and so pushes the industry into the hands of those companies and individuals who are politically connected or who can afford the lawyers to help them acquire the license.
Reminder that this is coming at a time where Antpool has almost 50% of the hashrate. If mining is jeopardized in the US then expect Antpool to have well over 50%. Now is the time to raise awareness and share your concerns with policymakers.