This is complex topic but I believe there are many ways trump can impose ban to tether like not allowing the use of dollar to peg their USDT and I agree that ETH value will plummet if stablecoin suddenly vanish.
Otherwise when will bitcoin gets its own stable coin on its own layer 2 to compete with ethereum? Layer 2's none of that sidechains nonsense that leverage no security from layer 1's.
There are plenty of L2 with its own stable for bitcoin, but never truly get the spotlight because people trust bitcoin much more than those L2 and if they want to do smart contract related activity they go to ETH where liquidity is not scarce compared to L2.