I’d rather have a tinge of alarmism about holding on to what matters in the U.S. than the alternative of being cavalier with my own rights, or with the rights of others.
As for institutions: they existed in Nazi Germany. The Jews were not instantly thrown into concentration camps upon the election of the NSDAP. It was a slow trickle, and it was done as much through law as through lawlessness.
There was a whole period (1933 to 1935) before Aryans and Jews were first legislatively defined by the Nuremburg Laws — mostly to deal with the consequences of Jewish assimilation — and then there was a slow trickle of both legal and extralegal measures used until the assassination of Vom Rath became a pretext for the Final Solution.
There was also a whole complex legal theory justifying the state of exception where Carl Schmitt, as a legal scholar, justified murder in such cases as the Night of Long Knives (in which Hitler was painted as protecting the state from dangerous S.A. elements) as well as the Commando Order (in which the SS were permitted to kill Allied intelligence operators).
It is easy to dismiss this all as having been dealt with by the Nuremburg Trials, but Schmitt’s writing was already rehabilitated and cited back during the Bush administration by Alberto Gonzalez and John Yoo. If you think Trump will be better than that, fine, but this stuff has already infected the American body politic. The question becomes, how do we manage the breakout?