It’s completely unrealistic in the short term, more so in the long term. This would require arresting millions of people - there simply isn’t enough jail space. They would have to execute people on sight, and that’s also not realistic because low level soldiers would refuse (there’s a reason the nazis needed to build a system instead of just executing jews on sight). Obviously if this were attempted it would result in extremely violent resistence which would destroy any economic, political, or other incentives for such an action.

Instead we can see what happened in Russia for a more realistic example - there was a slow elimination of dissent. Even today there are some Russians who vocally oppose Putin and don’t get arrested so long as they stay small enough. And that’s in a place where the society never had a culture of freedom to begin with, so here it will probably be much harder and obviously MAGA is much dumber than the Russians too. But regardless that’s why it’s very important to be vocal now and oppose any silencing of dissent, like the removal of pro-Palestine activists here on green cards. It may not affect you now, but if they keep at it for a decade or two it’ll get to you eventually.