Republican presidential candidate Donald Trump. (Jabin Botsford/The Washington Post)

The writer is a political theorist at Harvard University and a contributing columnist for The Post.

Since my column Sunday arguing that we, the people, ought to unite to block Donald Trump, a highly successful demagogic opportunist who is taking advantage of a divided country, I have, as you might imagine, received a great deal of correspondence. You can read a sample here. (Be forewarned that you’ll find obscenities, though they are not mine.) I have, however, also had the pleasure of an extended, quite civil email correspondence with one Trump supporter, and this has helped me further clarify my views.

Our conversation reached an interesting point when I asked him, “What could actually make you change your mind about Trump? That is, if your hypothesis is that Trump would be a good president, what would actually refute that hypothesis for you? If you didn’t mind sharing your thoughts on that, I would be very grateful.”

He responded (I promised that I would only paraphrase, and not quote, him) by saying that he would conclude that Trump hadn’t been the right choice if Trump ever made good on his promises to ban Muslims generally from entering the United States or to deport people whose only crime is being in the country illegally. He takes all those proposals to be pure performance. He believes he can count on Trump to undo President Obama’s executive orders and to block the admission of refugees from dangerous places, and that that’s as far as it will go.

Then he turned the question back on me, asking what would make me change my mind. Let’s say that Trump becomes president, he asked, and the kinds of things I fear don’t happen. Would I change my mind and agree that I had blown things out of proportion?

I slept on his question for a night and then gave him this answer:

The things I fear are already happening.

This country has seen a rise in white supremacy groups since 2000, as the Southern Poverty Law Center has documented. This is the first election in which their organizational power has propelled a candidate to durable prominence, even if that candidate has now also attracted lots of other kinds of supporters. Even after Obama released his long-form birth certificate in 2011, about 23 percent of Republicans continued to hold the view that he was born overseas. In September, 61 percent of Trump’s voters were “birthers.” Exit polling from the South Carolina primary last weekend showed that 70 percent of Trump’s voters in that state wish that the Confederate battle flag still flew over their statehouse. Although Sen. Ted Cruz (R-Tex.) comes close, no other candidate draws at this level from this constituency.

I study the impact of digital technologies on civic participation, and I have been watching groups of this sort form and grow in strength for some time, improving their capacity for coordination. These voters have given Trump his hard granite floor of at least 20 percent to 25 percent support.

But their success at propelling their candidate to prominence was possible only because of the fragmentation of the rest of the Republican electorate. A share of 20 to 25 percent of Republicans wouldn’t have been enough to do that if in August or September there had been only one or two others in the race. Trump counts votes with the best of them; he saw his opportunity and ran with it.

Donald Trump won the Nevada GOP caucuses on Feb. 23. Here's how. (Peter Stevenson/The Washington Post)

His success is now providing affirmation and cover to his base of nativists and organized white supremacist groups. Such groups are connected to traditions of mob violence (consider the history of this country from the 1910s through the 1970s). This is why Trump’s suggestions that maybe protesters should be roughed up or punched are so loaded. This is the context in which to hear his celebration of false historical narratives about the use of “bullets dipped in pig’s blood” for the summary execution of Muslim adversaries. In the context of our very own history, Trump’s habit of condoning lawlessness is dangerous. When political leaders condone violence, their words are already doing things. They provide cover, embolden and enable.

My interlocutor suggested that lawlessness has been an issue in the Obama administration, too, as with excessive IRS scrutiny of the tea party. I agree with him that this was an example of unjustifiable overreach. My commitment is to the rule of law and its nonarbitrary application.

The question of how words that condone lawlessness relate to lawless actions is always delicate. Over the years, I have gotten my share of hate mail, but never have I gotten anything as ugly as what I received in response to Sunday’s column. How should I understand the shift in the level of rhetoric? The period from 2004 to 2012 saw increases in religiously based hate crimes and hate crimes against Latinos, according to Bureau of Justice Statistics. Since the Paris attacks, hate crimes against Muslims have been rising. Clearly, the mere fact of a terrorist attack is enough to explain that, but Trump’s words are certainly not helping to reverse the tide.

My conclusion, then, was that I would have to concede that I had been wrong about Trump if under a Trump presidency: 1) the rising tide of white supremacy turned; 2) the country secured its capacity to protect the rights of Muslim Americans; 3) the immigration issue were handled with reasonable compromises and without mass deportations (I can’t believe I even have to write that); and 4) constitutional rights, including freedom of expression and association, were concertedly and consistently protected for everyone. (Since many of my correspondents have questioned whether my commitment to equal rights includes white people, let me say affirmatively that I mean “everyone” in its standard usage, which, yes, does indeed include white people.)

It turns out that for me, the question of what Trump stands for is not a matter of trying to predict what will happen; it’s about observing what is already happening. It also turns out that for me to conclude that I was wrong about Trump, he would have to do the opposite of what he says he is going to do.

My conversation with my correspondent did convince me, though, that there must be another side to Trump, so I tuned in Wednesday to his Regent University event with Pat Robertson. Was Trump just a corporate tough — like Steve Jobs and Larry Ellison — who had learned to rumble in a certain kind of environment, but beneath whose tough exterior there is affable charm and a good heart, as my conversational partner argued? Indeed, Trump put in a very different performance than I had seen before. As he promised after South Carolina, the obscenities were gone. He has suggested that for the general election, he would tone his performance down, and he did just that for this evangelical audience. He even provided a dramatization of the difference between his “tough” mode and his “smooth” mode and explained why he thought the second was better sometimes. He told lots of stories, made lots of jokes and stuck to his core message (“How do you define a country if you don’t have borders?”). He is a brilliant performer.

This is what makes Trump truly dangerous. Having established a rock-solid relationship with an aggressively ethno-nationalist base, he is ready to pile on the charm to bring everyone else on board, while also seeking to intimidate those who disagree with him. But note, the only people to whom he has made any kind of consistent commitment, through repeated signaling, are those birthers and nativists with whom he began his journey. The decision about voting for Trump is a choice about whether to give that base its most significant electoral victory in a very long time.