[Epistemic status: I know nothing about politics. This post written in the spirit of being wrong loudly.]
Here is my understanding of possible situations in which Trump could be significantly worse than Generic Republican President.
I think Trump is extremely high variance: I think possible outcomes from his presidency range from “better president than Obama or Hillary Clinton” to “nuclear war”. Needless to say, this is a very safe thing to say as a predictor, because if he turns out to be a great president I can say “look! I said he was high-variance!” and all I have to do is give up I-told-you-so points that won’t matter all that much anyway if we’re scavenging in a nuclear wasteland.
Trump is high variance for a couple of different reasons. First, he has not held any political office; this means that we don’t have any sense of how he governs (whether he will listen to advisors, whether he will try to keep his campaign promises, whether his impulsive behavior will be sobered by the power he holds, etc.). Second, he doesn’t know anything about governing, which increases the likelihood that he will make totally random and ill-informed decisions out of ignorance. Third, over the course of his campaign, he has often been extremely vague about his preferred policies beyond “terrific” and “the best.” He has regularly gone back and forth about what his positions are. When he does express policy positions, they are often more symbolic than literal. That is, “I want to register all the Muslims” may mean “I take the threat of Islamic terrorism seriously”, not “I want to create a large database of every Muslim”. All this makes a bit hard to tell what he will actually do.
That said, I think it’s worth trying to figure out what the most likely worst-case scenarios are so we can plan ahead.
Since I’m comparing Trump to the generic Republican president, I am not including policies where I also expect the generic Republican president to be horrible, such as not allowing refugees into the country.
There are several things that people are worried about that I am explicitly not worried about. For instance, Trump is relatively pro-LGBT for a Republican (his Ballotpedia entry has a pretty good overview). While Pence is fairly anti-LGBT, I would view Pence being able to pass anti-gay policies as a positive sign, because it would suggest that Pence has actual power and Pence is way lower-variance than Trump. While anti-LGBT laws are awful, we’re only like four percent of the population, and I would much rather have federally funded conversion therapy than a trade war, which hurts everyone, queer and not queer. (In the long run, of course, Supreme Court justices have effects; we can only hope that Pence will follow in Eisenhower’s footsteps and accidentally nominate Earl Warren.)
I do not care about the president’s personal virtue. I do not think it is particularly important for my assessment of his presidency that Trump has committed repeated sexual assaults; Bill Clinton is a rapist, but I think he did a decent job as president. I also am uninterested in questions about Trump’s personal feelings of racism. I don’t think it would be a whole lot of comfort to a Latino deported from the only country he’s ever known that Trump harbors no personal feelings of animosity to him in his heart.
So here are the scenarios I can think of for Trump being a really bad president:
Trump is incompetent at his job. Several aspects of being president are very complicated and tend to break a lot of things if you do a bad job at them. I’m thinking in particular of international relations and macroeconomics. Macroeconomic policy is fairly complicated and has a large effect on people’s wealth and quality of life. In addition to mismanagement due to incompetence, Trump might mismanage the economy for his short-term political benefit at the expense of long-term fiscal health.
My understanding of diplomacy is that it is extremely important to be predictable and to send clear messages to avoid misunderstandings that could lead to wars; Trump neither has political experience in which he has developed these skills nor has he shown a great ability to be predictable and a clear communicator on the campaign trail. I also worry about Trump being rash and easily offended, which leads to him escalating tense situations. This is where Trump’s largest chance of being an existential risk comes from, I think.
Positive signs: Trump appoints to his cabinet competent people who are not sycophants, preferably including at least one #NeverTrumper; Trump appoints qualified people to the Fed; over his first year in office, Trump has a cool-headed and moderate foreign policy.
(This, incidentally, is why I do not think we should nominate Oprah, or Kanye, or Bruce Springsteen, or the Rock, or any other celebrity. An unqualified Democrat is as much of an existential risk as an unqualified Republican.)
Trump has bad policies. My primary concerns are about immigration, climate change, prisons, and trade.
I think it would be bad if he made a serious attempt to deport a large percentage of undocumented immigrants. Given that undocumented immigrants are three percent of the US population, I’m not sure that deporting more than a small minority of them could be done without serious human rights violations. I also think it would be bad to sharply reduce the number of immigrants the US takes in, because immigration benefits migrants a lot.
I am worried about Trump ending trade deals which benefit people in developing countries. I am particularly worried about Trump’s anti-trade stances and poor diplomacy skills precipitating a trade war, because trade wars hurt everyone but particularly the poorest, and this would lead to an increase in international tension that may lead to a real war.
The United States has about a fifth of the world’s prisoners, which makes our prison policy unusually important. Trump has nominated Senator Jeff Sessions as Attorney General. Senator Sessions was one of only a handful of senators who voted against an amendment banning torture of prisoners; while that amendment applied primarily to the Department of Defense, I think it speaks to his respect for the humanity of people who might have done something wrong. He is also well-known for being against marijuana use, going so far as to say last April that good people do not smoke marijuana. I am afraid that Senator Sessions will not pay an adequate amount of attention to the human rights of prisoners and drug users, that he will expand the drug war, and that he may seek to imprison consumers of legal marijuana.
I am also concerned about Trump radically cutting back or even eliminating US policy that is intended to prevent or reduce the harm of climate change, because climate change is predicted to kill lots of people, especially the global poor.
Sessions was a bit of a surprise to me, so I am also worried about Trump choosing other advisors that have remarkably awful positions on important issues.
Positive signs: Trump shows a willingness to break campaign promises; Trump implements some of his campaign promises in a less extreme form (e.g. expanding the border fence somewhat and then claiming that’s a “wall”); Trump appears to focus on relatively innocuous policy positions (e.g. building a lot of infrastructure and naming it after himself); Sessions is not appointed Attorney General; the rest of Trump’s cabinet is non-awful.
Trump is an autocrat. This is the “Trump as Juan Peron” theory, as written about eloquently in this article. In this scenario, Trump causes a good deal of harm to America’s institutions. We might expect jailing of political opponents, punishment of protestors, firing of advisors who disagree with him, disrespect of the free press, and general silencing of dissent. He might be unlikely to give up power once his two turns are up and continue to rule through proxies. An autocratic Trump administration would also likely have batshit economic policy, because autocrats usually do. The autocrat scenario leads to a good deal of harm to America’s institutions, possibly leading to the fall of America as a great power.
Even if Trump’s autocracy is successfully contained by the strength of America’s institutions– for instance, if he tries to interfere with the freedom of the press, but the Supreme Court slaps him down– he may inspire authoritarian and autocratic movements in other countries.
Positive signs: A year into his presidency, Trump continues to be no more prone to jailing political opponents or punishing protestors than the average American president (note that early positive signs may simply be Trump biding his time); early attempts to gain power are met with strong opposition from Republicans.