This observation is crucial but it overlooks the fact that Republicans just did exactly this. Republicans had control of a legislature and used it's subpoena power to prevent a Democrat from winning the election. It's reasonable to imagine that they will do the same if a strong Dem shows up again.
"But the biggest danger arising from unified Republican government isn’t that it will enact bad policies that might be repealed later. It is that the GOP will use its moment at the apex of power to ensure that it can never be displaced from this position."