Other points are perhaps more disputable -- his "all-too-plausible" account of how Trump could became a tyrant strikes me as quite doubtful, for instance, since it requires a Trump administration acting far more coherently than we currently have reason to expect it could, arguably overestimates the ability of Trump supporters to organize on command, and simply fails to consider the sheer inertia that has to be overcome to move the U.S. federal government apparatus to consistent action, as well as the inertia of a population of over 300 million. An American coup is far more likely to arise out of opportunistic use of an unrest that spreads first at the bottom than from any actions initiated from the top.
And there are other points that are simply bad framing -- as Alyssa Rosenberg has noted, for instance, you should not confuse resistance with ordinary civic responsibilities. Gowder violates this commonsensical principle throughout.
But actually I want to focus on one thing:
Similarly, we must aggressively use the institutions of liberal democracy that we do control to sanction antisocial behavior. Jurisdictions controlled by opponents of Trump must make the investigation and punishment of hate-crimes, alt-right harassment, and similar behaviors a top priority—those who would engage in violence, or criminal activity that is a precursor to violence (stalking, hacking, doxxing, etc.) against opponents of the regime must instantly learn that they cannot act with impunity, and those who might otherwise be intimidated by the prospect of these acts need to learn that they will be protected.
I have no idea what Gowder was thinking in writing this atrocious paragraph. This is not how one protects and upholds the rule of law; "aggressively" using institutions that you "control" in order to "sanction" behavior is the very opposite of rule of law.
(1) In a genuine rule-of-law regime, punishments by institutions must occur (i) according to consistent principles that are part of the institutions themselves and that (ii) have been legally established so that (iii) they are the responsibility of the whole of society rather than particular factions in it. Gowder's description violates all three of these -- it makes the punishments in question depend on the will to exercise power rather than on stable principles built into the institutions, it makes them decided upon by the initiative of the individuals in "control" of the institutions rather than by legal process, and it makes it explicitly a matter of one faction taking action against other factions. This is atrocious. It is a recipe for escalation of political violence rather than preservation of rule of law. No rational person wanting to uphold the rule of law says, "We need to use the public institutions we control to punish people who are threats." It does not matter what the threats are, or how good the intentions are; it is a usurpation of power and the replacement of rule of law with the agenda of a faction.
(2) You should never use public institutions aggressively to punish people. Punishing people is a very serious matter, one that must be done cautiously and according to a proper form and process that provides the person who might be punished with multiple forms of protection. This is not something that can be done "aggressively". One might as well talk about aggressively going through a detailed safety checklist.
(3) Punitive institutions in a liberal democracy are not to be used for agendas, but instead should act in consistent ways for the common good of the whole, according to their specific mandate. If you are talking about someone using public institutions in order to punish people, you are already on the wrong track. In the same way, if there is any sense in which a faction controls an institution that does not boil down to "they happen to perform the official roles that are to be performed in much the same way regardless of who is performing them", you are talking about institutions that have already been corrupted. To be sure, there is always some wiggle room for different priorities and for judgment calls, but if the internal and intrinsic behavior of an institution significantly changes depending on who happens to be running it, this is already a sign of corruption, since the behavior should primarily be governed by the law. Rule of law requires that impartial and objective law be reflected by impartiality and objectivity in the functioning of the institutions of the society.
(4) The one-sidedness of Gowder's characterization is also a bit chilling. The institutions of a liberal democracy are there to protect everyone. If you are upholding the rule of law, then they should not only be used to protect opponents of the regime from violence but also supporters of the regime from violence. It should be entirely a matter of indifference whether you personally support or oppose the regime: the protections should be the same because they are the shared protections of everybody. Anything else turns rule of law into a war of one faction against another.
There is nothing less conducive to social trust than talking up the importance of it in an article in which you simultaneously advocate the use of public institutions that you 'control' to punish people aggressively. I have noticed this self-defeating pattern in other Trump opponents -- talk up some principle of liberal society and then pass immediately into saying something so utterly illiberal and inconsistent with it as to be truly astounding. (I have noticed this a number of times in how people talk about the civil service, for instance, as well as in how people talk about street violence for political ends.) Obviously this is not helpful for anything; indeed, it is an inconsistency dangerous to everyone.