I'm an American. I hate what is happening. Even if I may support the underlying policy. I've no concerns about deporting people who are not legally authorized to be here. But it makes no sense to deport folks who have been in this country and contribute to society. Criminals, sure. Folks just trying to have a better life, it's terrible.
I'm in a pretty liberal State. Republicans here often describe ourselves as "California Republicans" because we love good tax policy, but also think abortion is essential to women's bodily autonomy. Some of us are religious, but not radically so.
Trump is gone in 2+ years. The American system is strong. Even die-hard republicans would oppose ignoring judicial rulings are congressional legislation.
But we've seen this before. Trump isn't the first president to behave as if the Executive branch has significant power. Nixon was in this camp. W. as well. But even those who support a strong executive understand that the US constitution defines 3 "co-equal" branches of government.
Another factor is State vs. Federal jurisdiction. "Trump is going to cancel the midterms!" Yeah, no. Elections are run by individual states and the feds aren't going to have much luck convincing California to cancel elections.
Mainstream republicans love the Constitution and believe it must be honored. Justice is achieved through fair and free process where every citizen has the same legal protection. If Trump tries to push this too far, he will absolutely lose support from the majority of Republicans. The radicals on the Right do not represent mainstream American conservative thought, IMO.
As an example, a few years ago the feds tried to enforce federal law on pot. This mean sending agents to interfere with shops in my state. When my republican buddies learned of this, we organized and surrounded the pot shops to prevent feds from entering. The 10th amendment is clear. Any power not given to feds explicitly, is controlled by states.
Outside the US, I don't know if there is an appreciation for how much power individual States have. Sure, there is the supremacy clause. But States beat feds all the time by showing that they don't have constitutional authority on what they are trying to enforce.