So, they're finally here. After months of anxious preparation here in our city, the Republican National Convention has come to Cleveland. The city is as carefully groomed and as nervous as a teenager before the prom. The pedestrian walk on East 4th Street is filled with broadcast booths. High-end restaurants have turned into the temporary headquarters of Bloomberg or Twitter. The park in Public Square has been completely, and beautifully, renovated; we had to close it down for more than a year. The construction scaffolds are finally gone from Euclid Avenue, but new traffic barriers and fences are up. It's impossible to know which roads will be blocked off, where you can drive and where you can't. I won't be going back downtown until this is over. I'll be up in the Heights, holding my breath.

What goes on in the convention hall doesn't concern me. If the Republican Party and its loathsome nominee want to screw up on national television, that's their business. What happens in the streets matters enormously. We're trying to build this city up. We really don't need any additional trouble.

So I'm worried about protests turning into confrontations, because peaceful demonstrations can attract hangers-on who have no peaceful intentions. I'm worried about violent opportunists, including various lone-wolf lunatics, who might choose Cleveland as a target to attack. I'm nervous about a police department with some ugly recent history being put on edge by recent attacks against police. I'm downright terrified by the open-carry activists who have apparently already taken to standing in Public Square with goddamn AR-15s, basically insuring that nearly anything that goes bad will go worse. And I'm nervous that pro-Trump demonstrators will look for an excuse to go after Black Lives Matter or other anti-Trump demonstrators. One of the things that's scary about this situation, and different from previous conventions, is the possibility of ideologically-opposed demonstrators looking for a brawl.

The good news is that many of the armed and/or truculent fringe groups who previously planned to descend on Cleveland to declare their allegiance to "protect" Trump and his followers, have now decided to skip the show. I'm more than happy that the Oath Keepers, the white supremacists, and the Bikers for Trump won't be arriving. (h/t to the great JJ Macnab's Twitter feed for providing updates on these groups). I watched the head of Bikers for Trump on the local news this week, raving about "protecting" Trump and "protecting" the police and keeping anti-Trump protestors in line. That, obviously, is the most brilliant event-safety idea since the Rolling Stones hired the Hell's Angels to provide concert security at Altamount. (To give Donald Trump his very limited due here, he did not explicitly invite any of these yahoos to Cleveland, while Mick Jagger actually went out and hired the Angels.) But the Bikers for Trump guy could not get a parade permit, so he's not coming. That gust of wind you hear in the trees is my sigh of relief, all the way from Ohio.

We're at a tense moment when people are wondering if we can maintain our civil peace and our democracy, when we can no longer entirely avoid the debate over whether or not Trump represents a genuine American fascism. That argument is endless, because "fascism" has never been especially well defined, but I do want to point to one thing we should look out for.

Authoritarian regimes generally, and fascist regimes specifically, tend to have a body of irregular, semi-official thugs, separate from the official security forces. Those groups conduct most of the violence and intimidation. Hitler had his brown shirts, the original Storm Troopers; Mussolini had his black shirts. But tyrants with different ideologies often have the same groups: the Duvalier regime in Haiti had its tontons macoutes, the Iranian mullahs have their "people's militia," the basij. The Rwandan genocide against the Tutsi was conducted by local militia. The Klan, a nominally secret society, carried out terrorism against southern blacks from the 1860s through the 1960s. Dictators don't necessarily send the army or the police. They often have these irregular groups to break windows and bust heads outside the official apparatus of power, and to help keep that apparatus in the tyrant's hands.

Donald Trump is, at best, a racist demagogue with no respect for the Constitution. He is a real danger to American democracy. But so far, he has not mobilized the support of any irregular or paramilitary forces. Should that ever happen, it will be a sign that things have taken a hard turn for the worse.

Trump has had some impromptu violence at his rallies, which he has both incited and pretended not to incite. But violent rally-goers have not yet formed any organization. So far they're just one-time, single-use mobs, and the Trump campaign doesn't necessarily have the skills or discipline to organize them as campaign volunteers, let alone as a paramilitary auxiliary. There are plenty of unsavory folks around Trump, but -- thank heavens -- he doesn't have an Ernst Rohm.

There are also pre-existing paramilitary groups who are clearly excited by Trump and willing to follow him: the Oath Keepers, the Three Percent Militia, and various white supremacist types including some chapters of the Klan. The actual capacities of these groups, as opposed to their fantasies, are not really clear. But these are people who talk about various kinds of action to promote their ideologies, and extra-legal violence is part of their ideology.

The Trump campaign has not taken these groups on board. Trump's own approach to them is the familiar one of winking disavowal: he clearly is happy for their votes, but will officially disavow them (he actually prefers the phrase "I disavow," with nothing else in the sentence) in ways the white supremacists apparently take as just window dressing. But Trump has not shown any interest in these groups busting any heads for him.

But if we reach a point where any of these groups, or a new group like them, starts to act in concerted ways to aid the Trump campaign: intimidating voters, vandalizing Clinton headquarters or wholesale trashing yard signs, then we'll have turned an ugly page. They might have some excuse or pretext, such as "fighting back" against the New Black Panthers or another group they call "thugs," but that will just be an excuse. And if Trump ever seems to give such behavior his ambiguous blessing, then it will be a genuine national emergency.