Without due process, you could be accused of being here illegally and shipped off to a prison in El Salvador and have no chance to plead your case.

Due process is not given to us as a right because we're US citizens. The framers of that document took it as a given that human beings have those rights.

The constitution is a required limitation on government officials. The reason officials swear an oath to it is that *they* are required to follow it, and not apply it selectively.