Showing up at Donald Trump rallies looking for an opportunity to fight with Donald Trump supporters, set Trump merchandise on fire, chant Mexican nationalist slogans, get into scuffles with riot police, and throw eggs at people is a bad idea. It is wrong, morally speaking, to inflict physical violence on a random person because that person happens to hold what you see as erroneous political beliefs.
And while a Trump presidency is in some respects a threat to the rule of law and the American constitutional system, it is also a threat that is currently well-contained by the conventional political process. Trump is currently a very unpopular person, and if some large fraction of the people who currently don't like Trump show up on Election Day and vote for his opponent, then he will lose.
It is certainly true that in the course of human events, political situations arise that cannot be adequately remedied inside the context of the legal electoral process. But there's no reason to think that this particular situation is one of those situations, and people living in a democratic society have an obligation to attempt normal political strategies before resorting to extreme ones.
On the contrary, the evidence is fairly clear that illegal anti-Trump activities are not an "extreme" tactic that may be justified by an "extreme" situation — they are a straightforwardly counterproductive form of venting that people interested in actually stopping Trump ought to avoid.
In the 1960s, riots boosted Republican vote share
Princeton professor Omar Wasow has a relevant paper that examined county-level voting patterns in the 1960s. What he found is that exposure to nonviolent protests pushed people to vote for the more liberal presidential candidate, while exposure to violent ones pushed people to vote for the more conservative candidate.
The effect is large enough, according to Wasow, that the series of riots in 1968 swung the election to Richard Nixon:
How do the subordinate few persuade the dominant many? This article links nonviolent and violent tactics employed by socially marginal protesters to conditional feelings of empathy or threat in the voting majority. I test this argument by estimating effects of black-led protest movements in the 1960s on white attitudes and voting behavior. In the 1964, 1968 and 1972 presidential elections, I find proximity to black-led nonviolent protests was associated with significant increases in countylevel Democratic vote-share whereas proximity to black-led violent protests caused a substantively important decline. In counterfactual scenarios of Martin Luther King Jr. not being assassinated and fewer violent protests occurring before the 1968 election, the Democratic presidential nominee, Hubert Humphrey, would likely have beaten the Republican nominee, Richard Nixon. This research has important implications for existing theories of social movements, political violence and voting behavior.
To be clear, the scale of rioting in 1968 was drastically larger than anything we've seen related to the Trump campaign. A meaningful electoral impact would require a major escalation of violence beyond what we've seen. But to the extent that clashes do ratchet up in scale, the evidence suggests they will help Trump.
UK riots boosted anti-immigrant sentiment
Looking to other Western countries, another perspective comes from Matt Goodwin, Mark Pickup, and Eline de Rooij, who looked at the 2011 riots in London. What they found is that exposure to rioting make people feel more threatened and pushed them to anti-immigration political views:
We were interested in seeing whether people felt more or less threatened after the riots. Feelings of ‘threat’ are especially important, as they have been shown to have powerful effects on public attitudes toward issues such as immigration and diversity, and also on voting behaviour. In short, if people feel more threatened then they are more likely to express prejudice toward other groups, favour more restrictive policies on issues such as immigration and support extremist parties.
At a broad level, our findings suggest that – in the aftermath of the riots – citizens felt more threatened. On the whole, respondents in our nationally representative sample were more likely to feel they were under threat after the riots. However, there are many different forms of threat. People may feel that their economic position is threatened, their security is threatened and/or that their wider society and culture is threatened. We found that not all forms of threat increased.
They find that there was no increase in perceived economic threat — people were not worried, in other words, that rioters were damaging their concrete material interests. Instead, the riots caused people to feel less physically secure and more concerned about British cultural decline.
The upshot was to shift people toward a more xenophobic politics:
This has had important consequences. Although people did not associate the riots with specific minority groups (whether Muslim/Black/East European communities), they were more prejudiced in their aftermath. Those who felt afterwards that their security was under greater threat were more likely to express hostile attitudes toward Muslims. Meanwhile, those who felt afterwards that wider British society and culture were under greater threat were more likely to express hostility toward Muslims and also Black and East European communities. So, whereas the riots were not associated in the public mindset with particular minority groups, they have nonetheless increased prejudice in British society.
The UK and the US are different countries, and findings from one may not carry over to the other. But the broad structural situation seems similar, and the evidence suggests that politicized disorder pushes people toward more Trump-style politics.
Leftists are playing with fire here
A few left-wing commentators, alienated from mainstream liberalism by a mix of ideological conviction and annoyance at the course of the 2016 primary, have decided that the time is right for contrarian takes on this.
Amber A'Lee Frost, for example, says that given liberal alarm about the possible implications of a Trump presidency, it's hypocritical to condemn a street-fighting response:
Dems, Lib Media: Trump is the end of the world!— Amber A'Lee Frost (@AmberALeeFrost) June 3, 2016
Ppl: We'll fight em in the streets!
D,LM: Wait we just meant write thinkpieces & vote for us
And Corey Robin argues political violence is sometimes a useful tactic:
I have no idea whether this account of Chilean history is accurate. But these lines of argument strike me as clearly inapplicable to the actual political situation in the United States in 2016. Donald Trump is currently viewed unfavorably by 58 percent of the population, and he's losing in general election polling by 4 or 5 percentage points. Trump is not a military dictator or even the holder of any office at all.
I majored in philosophy in college and am happy to agree that it might be fun to debate a thought experiment in which throwing eggs at random rally-goers and setting hats on fire was the only thing stopping the democratic election of a fascist politician.
But none of the factual predicates for that thought experiment are true, so there's little point in confusing people about the actual stakes. Conventional politics is very likely to beat Trump, and a rising tide of lawlessness is one of his more plausible routes to winning.