The power of the executive is constrained, ultimately, by what people let them do. Including people inside the executive branch -- the people who're doing the arresting, transporting the prisoners, gunning down the protesters, etc. There's a lot of people involved who aren't committed to some authoritarian project, they're just... doing their job. They can be swayed by vibes, and general unpopularity of the regime.

The alternative to this view is either giving up or preparing for armed struggle. It's certainly possible that we could get there, but I don't think it's guaranteed yet.

(I acknowledge that this position is quite the blend of optimism and cynicism.)